•ODSRN 

1 1 PIK  PRODUCTS 


LUCIUS  L.VM  SliTF, 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA 


Glass 


THE   ORIGINAL   BABCOCK   TESTER 


Modern  Methods 
of  Testing  Milk  and 
Milk  Products 


A  HANDBOOK  PREPARED  FOR  THE  USE  OF  DAIRY 
STUDENTS,  BUTTER  MAKERS,  CHEESE  MAKERS,  PRO- 
DUCERS OF  MILK,  OPERATORS  IN  CONDENSERIES, 
MANAGERS  OF  MILK-SHIPPING  STATIONS,  MILK- 
INSPECTORS,  PHYSICIANS,  ETC.  :::  :::  :::  :::  ::: 


By 

LUCIUS    L.  VAN  SLYKE 

Chemist  of  the  New  York  Agricultural  Experiment  Station 


ILLUSTRATED 
REVISED    EDITION 


NEW   YORK 

ORANGE    JUDD     COMPANY 

LONDON 
KEGAN  PAUL,   TRENCH,   TRUBNER  &  Co.,   LIMITED 

1907 


OF  THE 

f    UNIVERSITY 


COPYRIGHT,  1906.  1907,  BY 
ORANGE  JUDD  COMPANY 

All  Rights  Reserved 


[ENTERED  AT  STATIONERS'  HALL,  LONDON,  ENGLAND] 


PREFACE 

To  attain  the  highest  degree  of  success  in  the  pro- 
duction of  milk  and  in  the  manufacture  of  its  pro- 
ducts, it  has  become  essential  to  acquire  some  knowl- 
edge of  the  methods  of  testing  milk  and  milk  products. 
The  application  of  these  methods  to  dairying  has  re- 
sulted in  lifting  the  dairy  industry  to  a  higher  plane 
of  intelligence,  and  in  effecting  changes  of  great 
economic  importance,  among  which  may  be  briefly 
mentioned:  (i)  Greater  justice  rendered  milk  pro- 
ducers in  paying  for  milk  according  to  its  quality.  (2) 
Prevention  of  large  losses,  once  very  common,  in  the 
manufacture  of  butter  and  cheese.  (3)  Improvement 
of  methods  of  manufacture  through  better  control  of 
details.  (4)  Increase  of  yield  of  products  made  from 
a  given  amount  of  milk.  (5)  Improvement  in  the  uni- 
formity and  quality  of  manufactured  dairy  products. 

This  little  book  has  been  prepared  for  the  use  of 
dairy  students,  cheese-makers,  butter-makers,  produc- 
ers of  milk,  operators  in  condenseries,  managers  of 
shipping-stations,  milk-inspectors,  and  others  inter- 
ested. Physicians  who  are  specialists  in  infant-feed- 
ing will  find  the  book  useful  in  testing  human  milk  as 
well  as  cows'  milk  that  is  modified  or  to  be  modified. 

No  previous  chemical  training  is  required  for  oper- 
ating successfully  the  methods  described.  Any  intel- 
ligent person  who  can  labor  with  painstaking  patience 
and  appreciate  the  value  of  attention  to  little  details 
should  be  able  to  master  these  methods  with  a  rea- 


165149 


VI  PREFACE 

sonable  amount  of  work.  The  assistance  of  a  trained 
teacher  will,  of  course,  make  the  task  easier.  No  one, 
whatever  his  educational  preparation,  can  hope  to  use 
these  or  any  similar  methods  successfully  who  can 
not  or  will  not  follow  instructions  accurately  and  ex- 
ercise patience  in  mastering  every  minute  detail. 

In  the  preparation  of  this  work,  the  writer  has  tried 
to  keep  in  mind  the  following  points:  (i)  Accuracy, 
simplicity  and  clearness  of  statement.  (2)  Making 
prominent,  as  far  as  practicable,  the  reasons  for  each 
step  in  each  process.  (3)  Emphasis  of  common  diffi- 
culties and  instructions  for  overcoming  them.  (4)  Im- 
pressing students  with  the  necessity  of  precision  and 
care  in  performing . every  detail  given.  (5)  Selection 
of  the  methods  approved  by  experience.  (6)  Avoidance 
of  such  technical  methods  as  require  unusual  skill  or 
equipment.  (7)  Omission  of  unnecessary  details.  (8) 
Embodiment  of  the  results  of  the  most  recent  investi- 
gations. (9)  The  special  needs  of  those  for  whose  use 
the  work  is  designed. 

The  scope  of  this  work  is  far  from  exhaustive,  but 
the  methods  selected  are  given  with  necessary  com- 
pleteness. Chemical  methods,  requiring  elaborate 
equipment  and  extended  special  training,  are  purposely 
omitted.  Any  one  desiring  a  full  description  of  such 
methods  can  obtain  it  by  addressing  a  request  to  the 
U.  S.  Department  of  Agriculture,  Bureau  of  Chem- 
istry, Washington,  D.  C.,  asking  for  a  copy  of  "Meth- 
ods of  Analysis  adopted  by  the  Association  of  Official 
Agricultural  Chemists." 

The  methods  that  have  been  compiled  here  are  in 
large  measure  the  direct  result  of  the  work  of  our 


PREFACE  Vli 

agricultural  experiment  stations,  and  afford  some  in- 
dication of  the  direction  and  value  of  the  work  done 
by  these  institutions. 

In  the  preparation  of  Chapter  XIII,  valuable  assist- 
ance has  been  kindly  rendered  by  Mr.  George  A.  Smith, 
Dairy  Expert  of  this  station. 

L.  L.  VAN  SLYKE. 
New  York  Agricultural 
Experiment  Station,  1906. 


PREFACE  TO   REVISED   EDITION 

Two  editions  of  this  book  have  been  issued  within 
the  first  year  after  its  publication.  Before  printing 
another  edition  it  seems  advisable  to  make  some  ad- 
ditions that  have  been  suggested  by  friendly  criticism. 
A  section  on  the  "Sampling  and  Testing  of  Gathered 
Cream"  is  added  to  Chapter  V.  The  author  has  also 
rewritten  Chapter  XIV.  Gray's  rapid  test  for  water 
in  butter,  which  was  included  as  an  appendix  in  the 
second  edition,  is  transferred  to  the  body  of  the  book 
under  Chapter  VI.  For  the  marked  favor  with  which 
this  little  book  has  been  received,  appreciation  can  not 
be  expressed  in  any  way  more  substantial  than  by 
making  an  effort  to  keep  the  subject  matter  up  to  date. 

L.  L.  VAN  SLYKE. 
Geneva,  N.  Y.,  September, 


viii 


CONTENTS 


i 

Chemistry  of  Cow's  Milk  and  Milk  Products     ...         1 

II 
Methods  of  Sampling  Milk  . 20 

III 

The    Babcock    Test — Description    of    Apparatus    and 

Materials 32 

IV 
Method  of  Operating  the  Babcock  Test  ....  53 

V 
Method  of  Testing  Cream  by  the  Babcock  Test  .  .  69 

VI 

Methods  of  Testing  Skim-milk,  Whey,  Butter,  Cheese, 

etc.     .      . 81 

VII 

Methods  of  Testing  Acidity  of  Milk  and  Milk  Prod- 
ucts  ..-96 

VIII 

Methods  of  Testing  the  Bacterial  Condition  of  Milk     113 

IX 

Methods    of    Testing    Milk    by    Rennet-Extract    and 

Pepsin 121 

X 

Methods   of  Testing   Specific    Gravity  and   Solids   of 

Milk  by  the  Lactometer 127 


X  CONTENTS 

XI 

Methods  of  Testing  Milk  and  Milk  Products  for  Adul- 
terations      141 

XII 

The  Babcock  Test  applied  to  Farm  Conditions     .      .     151 

XIII 

Methods  of  Commercial  Testing  and  Scoring  of  But- 
ter and  Cheese 158 

XIV 

Methods  of  Commercial  Testing  and  Scoring  of  Milk 

and  Cream 182 

XV 

Arithmetic  of  Milk  and  Milk  Products     .....     193 
INDEX  215 


ILLUSTRATIONS 


PAGE 

The  Original  Babcock  Tester Frontispiece 

Composite-Sample  Jars 25 

Rack  for  Composite  Samples 26 

Sampling-Dipper 27 

Scovell  Milk-Sampler 27 

Equity    Milk-Sampler 27 

Milk-Testing  Bottle 34 

Milk-Measuring    Pipette       ...........  35 

Greiner's   Automatic    Pipette          36 

Wagner's  Pipette 36 

Acid-Measure 36 

Acid-Burette    and    Stand .  37 

Automatic    Burette 37 

Steam-Turbine  Tester 38 

Hand-Tester 38 

Small  Hand-Tester .      .  39 

Electric  Centrifuge 40 

Hydrometer  for  Testing  Strength  of  Sulphuric  Acid  43 

Milk-Bottle   Tester 46 

Testing  Accuracy  of  Milk-Bottle 46 

Burette  and  Support 48 

Waste-Jar  for  Emptying  Test-Bottles 50 

Test-Bottle  Rinser 50 

Test-Bottle  Draining  Rack 51 

Farrington's  Bottle-Cleaner — Bottle-Holder  Empty    .  51 

xi 


Xll  ILLUSTRATIONS 

Farrington's  Bottle-Cleaner — Bottle-Holder  Immersed  52 

Farrington's  Bottle-Cleaner — Bottle-Holder  Draining  52 

Correct  Way  of  Holding  Pipette  and  Bottle     ...  55 

Wrong  Way  of  Holding  Pipette  and  Bottle     ....  56 

Measuring  Fat-Column L.  63 

Automatic  Russian  Pipette 67 

Russian  Test-Bottle .  67 

Bulb-Necked   Cream-Bottle  ' 70 

Straight-Necked   Cream-Bottle .-  71 

Cream-Testing   Scales 72 

Cream-Sampling  Sieve 74 

Bottles  for  Testing  Skim-Milk 82 

Bottle  for  Testing  Butter 86 

Wagner's  Improved  Form  of  Gray's  Water-Test      .  91 

Mann's  Acid  Test 101 

Farrington's   Alkaline-Tablet   Test      ......  104 

Spillman's    Acid-Cylinder 105 

Purdue  Alkali-Test 107 

Hand-Centrifuge  for  Sedimentation  Work    ....  118 

Tube  for  Sedimentation  Work       .......  118 

Bausch  &  Lomb  Electric  Centrifuge 118 

International  Instrument  Co.'s  Electric  Centrifuge     .  119 

Glass  for  Collecting  Sediment  in  Milk 120 

Monrad  Rennet-Test 121 

Marschall  Rennet-Test 123 

Quevenne   Lactometer 130 

Cylinder  for  Lactometer 133 

Comparison  of  Different  Specific  Gravity  Scales     .      .  134 

Richmond's  Slide-Rule     .      .      .      .      .      .      .      .      .      .  138 

Butter-Trier  159 


UNIVERSITY 

OF 


Modern    Methods  of  Testing  Milk 
and    Milk    Products 


CHAPTER   I 

Chemistry  of  Cows'  Milk  and  Milk  Products 

THE  normal  milk  of  cows  contains  the  following 
compounds  and  classes  of  compounds : 

(1)  Water.  (4)   Milk-sugar. 

(2)  Fat.  (5)   Salts  or  ash. 

(3)  Nitrogen  compounds  or  proteids.      (6)  Gases. 

WATER 

The  water  present  in  milk,  however  much  its  pres- 
ence may  be  disguised,  is  the  compound  of  hydrogen 
and  oxygen  with  which  we  are  everywhere  familiar. 
The  water  in  milk  serves  the  purpose  of  holding  in 
solution  the  soluble  constituents  of  the  milk,  and  it 
also  acts  as  a  diluent,  better  fitting  the  mixture'  for 
animal  nutrition. 

Variation. — The  amount  of  water  normally  con- 
tained in  milk  varies,  depending  upon  such  conditions 
as  individuality,  breed,  stage  of  lactation,  age,  char- 
acter of  food,  amount  of  water  drunk,  state  of  health, 
etc.  In  the  case  of  single  milkings  of  individual  cows, 
the  water  may  vary  from  82  to  90  per  cent,  or  more. 
In  the  case  of  milk  from  herds  of  cows,  the  water 
varies  less,  usually  ranging  from  86  to  88  per  cent. 


2  MODERN    METHODS   OF   TESTING    MILK 

The  influence  of  breed. — The  following  figures, 
from  the  records  of  the  N.  Y.  Agricultural  Experi- 
ment Station  at  Geneva,  illustrate  the  influence  of  breed 
upon  the  water  content  of  milk : 

Per  cent,  of 
NAME  OF  BREED  water  in  milk 

Holsteiri  Friesian 88.20 

American  Holderness 87.35 

Ayrshire 87.25 

Short  Horn 85.70 

Devon 85.50 

Guernsey 85.10 

Jersey 84.60 

The  influence  of  lactation. — The  variation  of  water 
in  milk,  as  affected  by  advance  of  the  lactation  period, 
is  illustrated  by  the  following  figures,  which  cover  a 
period  of  ten  months  from  the  time  of  calving: 

,  Per  cent,  of 

MONTH  OF  LACTATION  water  in  milk 

i 86.00 

2 86.50 

3 86.53 

4 86.36 

5 86.25 

6 86.00 

7    •    ' 05.82 

8 85.67 

9 85.54 

10 85.17 

There  is  noticeable  a  general  tendency  for  the 
amount  of  water  in  milk  to  increase  for  the  first 
three  months  of  lactation,  after  which  there  is  a  con- 
tinuous decrease  to  the  end  of  the  lactation  period. 


CHEMISTRY   OF   COWS     MILK  3 

Total  solids. — Under  the  general  term  of  total  solids 
or  milk-solids,  we  indicate  the  constituents  of  the  milk 
other  than  water  (and  gases).  The  per  cent,  of  water 
in  milk  subtracted  from  100  gives  the  percentage  of 
milk-solids,  which  include  fat,  proteids,  milk-sugar 
and  salts  or  ash.  The  amount  of  solids  in  milk  varies 
with  the  same  conditions  that  affect  the  percentage 
of  water  in  milk,  but,  of  course,  in  just  the  reverse 
manner.  Most  states  orescribe  a  legal  standard  for 
milk-solids,  usually  12  per  cent.,  and  milk  containing 
less  than  the  legal  amount  is  regarded  as  adulterated. 

MILK-FAT 

The  composition  of  milk-fat. — Milk-fat,  also  called 
butter-fat,  is  not  a  single  chemical  compound,  but  is 
a  somewhat  variable  mixture  of  several  different  com- 
pounds called  glycerides.  Each  glyceride  is  formed  by 
the  chemical  union  of  glycerin  as  a  base  with  some 
acid  or  acids  of  a  particular  kind.  These  glycerin-acid 
compounds,  or  glycerides,  of  milk- fat  contain  about 
ten  different  acids,  some  being  present  in  small  propor- 
tions. The  four  following  acids  enter  most  largely 
into  the  composition  of  milk-fat,  in  the  form  of  their 
combinations  with  glycerin:  Palmitic  acid,  oleic  acid, 
myristic  acid  and  butyric  acid.  The  compounds,  or 
glycerides,  formed  by  the  combination  of  glycerin  and 
the  acids,  have  special  names  derived  from  the  acids; 
thus,  we  have  palmitin  (glycerin  combined  with  palm- 
itic acid),  butyrin  (glycerin  combined  with  butyric 
acid),  olein,  etc.  Milk- fat  contains,  on  an  average, 
about  40  per  cent,  of  palmitin,  34  per  cent,  of  olein, 
10  per  cent,  of  myristin,  6  per  cent,  of  butyrin,  and 


4  MODERN    METHODS    OF   TESTING    MILK 

from  less  than  i  to  nearly  3  per  cent,  of  each  of  tl 
glycerides  of  other  acids.  Milk-fat  contains  aboi 
12.5  per  cznt.  of  glycerin  in  combination  with  tl 
acids.  The  proportions  of  these  constituents  of  mill 
fat  vary  somewhat,  and  this  variation  influences  tr 
character  of  the  milk-fat.  Thus,  palmitin  and  myri: 
tin  tend  to  make  milk-fat  harder,  while  olein  and  but1 
rin  have  the  opposite  tendency. 

The  acids  contained  in  milk-fat  or  butter-fat  ma 
be  divided  into  two  groups:  (i)  The  acids  in  or 
group  (palmitic,  oleic,  myristic,  stearic,  lauric)  ai 
insoluble  in  water  and  non-volatile,  while  (2)  tl: 
other  acids  (butyric,  caproic,  etc.,)  are  more  or  le< 
completely  soluble  in  water  and  are  volatile.  Thes 
differences  afford  a  practical  basis  for  distinguishin 
pure  butter  from  artificial  butter.  Of  the  fat-acic 
contained  in  butter- fat,  about  87.5  per  cent,  consisl 
of  the  insoluble  fat-acids,  while  in  other  forms  c 
animal  fat  (beef- fat,  lard,  etc.,)  the  amount  of  thes 
insoluble  fat-acids  is  considerably  greater.  The  amour 
of  volatile  fat-acids  in  milk-fat  or  butter-fat  is  muc 
greater  than  in  other  forms  of  animal  fat. 

Fat-globules  in  milk. — Milk-fat  is  present  in  mill 
not  in  solution,  but  suspended  in  the  form  of  ver 
small,  transparent  globules.  Globules  varying  in  siz 
between  one  twenty-five  hundredth  and  one  fifteer 
thousandth  of  an  inch  in  diameter  are  the  ones  mo< 
commonly  present.  The  average  size  of  fat-globule 
in  milk  is  somewhat  more  than  one  ten-thousandth  c 
an  inch  in  diameter.  The  smaller  globules  are  mor 
numerous  than  the  larger  ones.  In  one  drop  of  aver 
age  milk  there  are  more  than  one  hundred  million  fat 


CHEMISTRY    OF    COWS     MILK  5 

globules.  Skim-milk  contains  fewer  and  smaller  glo- 
bules than  whole  milk,  while  the  reverse  is  true  of 
cream.  The  large  globules  do  not  differ  in  composi- 
tion from  the  small  ones.  The  size  and  number  of 
fat-globules  in  milk  are  influenced  by  such  conditions 
as  advance  of  lactation,  breed  of  cow,  food,  age, 
health,  different  milkings,  different  parts  of  the  same 
milking,  etc. 

It  was  formerly  believed  generally,  and  is  still  by 
some,  that  the  fat-globules  of  milk  are  surrounded  by 
a  membranous  covering,  or  else  by  a  semi-liquid,  al- 
buminous layer.  We  may,  however,  accept  it  as  es- 
tablished beyond  reasonable  doubt  that  the  fat-globules 
of  milk  have  no  special  covering  of  any  kind,  but  are 
simply  minute  particles  of  fat  floating  free  in  milk  in 
the  form  of  an  emulsion.  Fat-globules  quite  generally 
retain  their  individuality  even  in  butter  and  cheese. 

Amount  of  fat  in  milk. — Normal  milk  varies  greatly 
in  its  fat  content,  containing  from  below  2  to  over  10 
per  cent.,  if  we  consider  single  milkings  of  individual 
cows.  The  milk  from  herds  of  cows  varies  in  fat 
more  commonly  between  the  limits  of  3  and  5  per 
cent.  The  average  amount  of  milk-fat  in  milk  pro- 
duced in  this  country,  taking  the  true  average  for  the 
entire  year,  lies  somewhere  near  4  per  cent.,  perhaps 
a  little  under.  Many  of  the  conditions  that  affect  the 
percentage  of  fat  in  milk  are  fairly  well  known,  while 
others  are  little  understood.  We  will  briefly  consider 
some  of  the  well-recognized  conditions  that  influence 
the  fat  content  of  milk. 

(i)  Influence  of  individuality  of  cozv  on  fat  con- 
tent  of  milk. — It  is  uncommon  to  find  in  a  herd  of 


O  MODERN    METHODS    OF    TESTING    MILK 

cows  two  individuals  whose  milk  contains  the  same 
per  cent,  of  fat,  whether  we  consider  single  milkings 
or  the  average  of  many  milkings. 

(2)  Influence  of  breed  of  cozv  on  fat  content  of 
milk. — It  is  well  known  that  the  per  cent,  of  fat  in 
milk  varies   in  a   somewhat   characteristic   way   with 
the  kind  of  breed  of  cow.     While  there   is   marked 
variation  in  individuals  of  the  same  breed,   there  is 
found  to  be  a  fairly  uniform  difference,  more  or  less 
marked,  if  we  consider  the  averages  of  several  indi- 
viduals.     It   is   largely  owing  to   this   influence   that 
we  find  the  milk  of  one  country  differing  from  that 
of  another,  or  the  milk  of  one  section  of  a  country 
differing  from  that  of  another  section.     For  example, 
the  average  amount  of  fat  in  milk  in  Germany  and 
Holland  is  fully  one-half  per  cent,  lower  than  in  this 
country,  because  the  prevailing  breeds  of  cows  there 
are  those  producing  milk  comparatively   low   in   fat. 
The  following  figures,  taken  from  the  records  of  the 
New  York  (Geneva)  Agricultural  Experiment  Station, 
represent   averages   of   many   individuals    for   several 
periods  of  lactation:  Percent  of 

Average  Low£<  <^t 

Holstein  Friesian 3.36  2.88  3.85 

Ayrshire 3.60  3.20  4.24 

American  Holderness  ....  3.73  3.49  3.92 

Short  Horn 4.44  4.28  4.56 

Devon 4.60  4.30  5.23 

Guernsey 5.30  4.51  6.13 

Jersey 5.60  4.96  6.09 

(3)  Influence   of  age   of   cow   on   fat   content   of 
milk. — So  far  as  published  data  throw  light  upon  this 


CHEMISTRY    OF    COWS     MILK  7 

point,  there  appears  to  be  a  tendency  for  milk  to  be- 
come less  rich  in  fat  with  each  succeeding  period  of 
lactation,  especially  after  the  second,  though  individ- 
ual exceptions  are  not  infrequent.  More  data  are 
needed  to  settle  the  question  definitely. 

(4)  Influence  of  advance  of  lactation  on  the  fat 
content  of  milk. — In  general,  it  is  found  that  the  per 
cent,  of  fat  in  milk  increases  as  the  stage  of  lactation 
advances  after  the  third  month,  as  illustrated  by  the 
following  data   from   the   records   of  the   New   York 
(Geneva)  Station,  covering  10  months  from  the  time 
of  calving: 

NUMBER  OF  Per  cent,  of 

MONTH  OF  LACTATION  fat  in  milk 

I 4.54 

2 4-33 

3 4-28 

4 4-39 

5  .     •     . .  4.38 

6 4-53 

7 4.56 

8 4-66 

9 4-79 

10 5.00 

(5)  Variation   of   time    between   milkings   in   rela- 
tion to  the  fat  content  of  milk. — As  a  rule,  the  longer 
the  time  between  two  successive  milkings,  the  smaller 
is  the  per  cent,  of  fat  in  the  milk ;  and  the  shorter  the 
time  between  milkings,  the  greater  the  per  cent,  of  fat. 
When  the  time  between  milkings  is  uniformly  equal, 
the  variation  of  fat  in  milk  is  small,  provided  the  gen- 
eral environment  of  the  animal  is  the  same.     How- 
ever, as  there  are  not  commonly  such  entirely  uniform 


8  MODERN    METHODS    OF    TESTING    MILK 

conditions  of  surroundings  during  the  day  and  night, 
there  appears  to  be  a  common  tendency  for  the  pres- 
ence of  a  little  more  fat  in  the  morning's  milk,  even 
when  milkings  are  apart  the  same  length  of  time. 

(6)  Variation  of  fat  content  in  different  portions  of 
milk  drawn  from  the  udder. — The  following  figures, 
taken  from  the  writer's  records,  illustrate  the  general 
rule  that  the  first  milk  drawn  contains  least  fat,  the 
milk  last  drawn  (strippings)  being  the  richest  in  fat: 

Per  cent,  of  fat  in  milk 
cow  i     cow  2    cow  3 

First  portion  drawn  ....  0.90  1.60  1.60 
Second  portion  drawn  .  .  .  2.60  3.20  3.25 
Third  portion  drawn  .  5.35  4.10  5.00 

Fourth  portion  drawn  (strip'gs)     9.80        8.10        8.30 

It  is  also  known  that  the  per  cent,  of  fat  in  milk 
varies  in  different  quarters  of  the  udder  of  a  cow,  and 
also  varies  more  or  less  in  each  quarter  with  the  order 
in  which  the  teats  are  milked. 

THE    NITROGEN    COMPOUNDS    OF    MILK 

Some  confusion  prevails  in  respect  to  the  names  of 
the  nitrogen  compounds  of  milk.  They  have  been 
spoken  of  as  albuminoids,  proteids,  etc.  Frequently 
the  word  casein  is  erroneously  used  to  include  all  the 
nitrogen  compounds  of  milk. 

How  many  nitrogen  or  proteid  compounds  are  pres- 
ent in  normal  milk?  What  are  they?  Different  work- 
ers have  reported  from  one  to  seven  or  more.  The 
chemical  evidence  at  hand  justifies  us  in  the  belief  that 
fresh,  normal  milk  contains  not  more  than  three  or, 
perhaps,  four  nitrogen-containing  or  proteid  bodies, 


CHEMISTRY    OF    COWS'    MILK  9 

viz.,  casein,  albumin,  globulin  and  galactase.  Globulin 
and  galactase  are  present  in  so  small  quantities  that 
we  can  properly  regard  casein  and  albumin,  quantita- 
tively, as  being  essentially  the  nitrogen  compounds  of 
milk. 

Milk-Casein  is  the  most  important  nitrogen  com- 
pound in  milk,  because,  (ist)  it  is  the  one  present  in 
largest  quantity;  (2d)  its  presence  makes  it  possible 
to  convert  milk  into  cheese;  and  (3d)  it  has  a  high 
value  as  food.  Milk-casein  is  most  familiar  to  us  in 
the  form  of  the  solid,  white  substance  called  curd, 
which  forms  in  milk  when  it  sours  (though,  strictly 
speaking,  this  well-known,  white  substance  is  not  milk- 
casein,  but  casein  lactate). 

(1)  Composition  of  milk-casein. — Casein  is  a  very 
complex  chemical  compound,  containing  the  elements 
carbon,  oxygen,  hydrogen,  nitrogen,  sulphur,  and  phos- 
phorus.   In  milk  the  proteid  molecule  of  casein  is  com- 
bined with  calcium,  or  some  calcium  compound,  and 
hence    the    proper    chemical   name   of   milk-casein    is 
calcium  casein.     It  exists  in  milk,  not  in  solution,  but 
in  the  form  of  extremely  minute,  solid,  gelatinous  par- 
ticles in  suspension.     The  slime  found  in  the  bowl  of 
centrifugal  separators  consists,  to  a  considerable  ex 
tent,  of  milk-casein. 

(2)  Action  of  acids  upon  milk-casein. — When  milk 
sours  in  the  ordinary  way,  the  lactic  acid  formed  acts 
upon  the  calcium  casein,   two  definite  changes  taking 
place.     First,  the  lactic  acid  combines  with  the  cal- 
cium of  the  calcium  casein,  forming  calcium-free  ca- 
sein, or  simply  casein  set  free  from  its  combination 
with  calcium.     When  more  lactic  acid  forms,  the  sec- 


- 


IO  MODERN    METHODS   OF   TESTING    MILK 

ond  change  takes  place,  the  free  casein  taking  up  the 
acid  without  definite  combination  and  forming  a  sub- 
stance which  is  familiar  as  the  curd  of  sour  milk.  Sim- 
ilar changes  occur  when  milk  is  treated  with  other 
acids,  such  as  hydrochloric,  acetic,  sulphuric,  etc.  Free 
casein  is  insoluble  in  water  and  also  in  very  dilute  acids 
at  ordinary  temperatures.  The  action  of  acids  on  cal- 
cium casein  and  on  free  casein  is  hastened  by  increase 
of  temperature.  Casein  dissolves  easily  in  an  excess 
of  acid,  forming  soluble  casein  salts. 

(3)  Action  of  alkalis  on  milk-casein. — Dilute  solu- 
tions of  alkalis  (caustic  soda,  ammonia,  etc.)  act  upon 
casein  and  its   salts   with  acids,   forming  compounds 
that  dissolve  easily  in  water.     These  alkali  compounds 
of  casein  are  not  affected  by  rennet.     Some  of  these 
compounds  are  found  in  commerce  as  food  and  me- 
dicinal  preparations   under   such   names   as   Plasmon, 
Nutrose,  Santogene,  Eucasein,   Galactogene,  etc. 

(4)  Action  of  heat  on  milk-casein. — Heat  alone  un- 
der ordinary  conditions,  even  at  the  boiling  point  of 
water,  does  not  coagulate  the  casein  in  milk.     Casein 
may  be  coagulated  by  heating  under  pressure  at  a  tem- 
perature  of  about   270°   F.     The  browning  of  milk 
heated  under  pressure  is  more  or  less  due  to  changes 
in  the  casein.     The  formation  of  a  peculiar  skin  on 
the  surface  of  milk  heated  above   140°   F.  is  largely 
due  to  the  calcium  casein  of  the  milk  and  not  to  albu- 
min as  was  formerly  supposed.     The  skin  itself  con- 
tains practically  all  of  the  constituents  of  the  milk  and 
may  be  regarded  as  a  kind  of  evaporated  milk. 

(5)  Action  of  rennet  on  milk-casein.— One  of  the 
most  characteristic  properties   of   the   calcium   casein 


CHEMISTRY   OF   COWS'   MILK  II 

of  milk  is  its  coagulation  by  the  enzym  or  chemical 
ferment  contained  in  rennet,  which  is  an  extract  of  the 
mucous  membrane  of  a  calf's  stomach.  This  property 
makes  possible  the  manufacture  of  cheese  from  milk. 
The  curd  formed  by  the  action  of  rennet  is  called  para- 
casein  or,  more  properly,  calcium  paracasein.  There 
appears  to  be  little  or  no  chemical  difference  between 
calcium  casein  and  calcium  paracasein.  The  coagula- 
tion of  calcium  casein  produced  by  rennet  is  quite  dif- 
ferent from  that  produced  by  acids.  Calcium  paraca- 
sein behaves  towards  acids  and  alkalis  much  like  cal- 
cium casein. 

(6)  Other  changes  caused  in  milk-casein. — Under 
the  action  of  chemical  reagents,  of  enzyms  and  of  va- 
rious organisms,  calcium  casein  and  paracasein  may  be 
changed  into  a  large  number  of  other  substances. 
Among  the  compounds  and  classes  of  compounds  thus 
formed  are  paranuclein,  albumoses,  peptones,  amides 
(crystallizable  bodies)  and  ammonia.  These  products 
are  never  found  in  normal  milk  as  it  leaves  the  cow, 
but  may  be  present  in  milk  that  has  stood  some  time. 

Milk-Albumin. — Milk-albumin  differs  from  milk- 
casein  in  composition  and  behavior.  Thus,  milk-albu- 
min (i)  is  not  acted  upon  by  rennet;  (2)  is  not  coag- 
ulated by  acids  at  ordinary  temperatures;  (3)  is  co- 
agulated by  heat  alone,  though  not  completely,  above 
160°  F. ;  and  (4)  is  in  solution  in  milk. 

Milk-Globulin. — This  compound  is  present  only  in 
small  quantities  in  normal  milk  and  is  of  no  special 
importance,  so  far  as  known. 

Galactase. — This  substance  is  an  unorganized  fer- 
ment, or  a  mixture  of  such  ferments,  present  in  normal 
milk.  It  somewhat  resembles  pepsin  in  its  action,  be- 


12  MODERN    METHODS   OF   TESTING    MILK 

ing  able  to  coagulate  milk-casein  and  then  digest  it 
or  make  it  soluble.  It  is  present  in  very  small  amounts 
in  milk  and  its  action  is  very  slow.  It  has  never  been 
isolated  from  milk  in  pure  form.  It  is  probably  a  nitro- 
gen-containing substance.  Our  knowledge  of  galac- 
tase  is  very  far  from  complete. 

Amounts  of  casein  and  albumin  in  milk. — In  single 
milkings  of  individual  cows,  the  casein  and  albumin, 
taken  together,  vary  from  2.5  to  6  per  cent,  and 
average  about  3.2  per  cent.  Milk-casein  varies  in 
amount  from  2  to  4  per  cent,  and  averages  about  2.5 
per  cent.  Albumin  varies  from  0.5  to  0.9  per  cent, 
and  averages  about  0.7  per  cent.  The  amount  of  ca- 
sein in  relation  to  albumin  varies  greatly.  On  an 
average,  milk  contains  about  3.6  parts  of  casein  for 
one  of  albumin,  or,  stated  another  way,  casein  consti- 
tutes about  80  per  cent,  of  the  nitrogen  compounds  of 
milk. 

The  amount  of  casein  and  albumin  in  milk  is  influ- 
enced by  many  conditions,  such  as  influence  the  gen- 
eral composition  of  the  milk,  among  which  are  individ- 
uality, breed,  advance  of  lactation,  etc.  As  the  lacta- 
tion period  advances,  there  is  a  general  tendency  on 
the  part  of  casein  and  albumin  in  milk  to  increase. 

Relation  of  fat  and  nitrogen  compounds  in  milk. — 
In  normal  milk  containing  over  3  per  cent,  of  fat,  the 
amount  of  casein  and  albumin  is  rarely  greater  than 
the  amount  of  fat,  especially  in  the  milk  of  herds  of 
cows.  When  the  per  cent,  of  fat  is  less  than  that  of 
the  nitrogen  compounds,  the  milk  may  generally  be 
regarded  as  skimmed,  especially  in  the  case  of  milk 
from  herds. 


CHEMISTRY    OF    COWS'    MILK  13 

MILK-SUGAR 

Milk-sugar,  also  called  lactose,  is  present  in  cows' 
milk  in  solution.  In  general  composition,  it  resembles 
ordinary  sugar,  but  it  is  less  sweet  and  less  soluble 
in  water.  The  amount  of  sugar  in  milk  varies  from 
below  4  to  over  6  per  cent,  and  averages  about  5  per 
cent.  Its  importance  in  dairy  work,  especially  in  con- 
nection with  the  manufacture  of  butter  and  cheese, 
comes  from  the  ease  with  which  it  is  converted  into 
lactic  acid  by  certain  forms  of  bacteria.  In  the  ordi- 
nary souring  of  milk,  the  amount  of  milk-sugar  de- 
creases somewhat  more  than  one-fourth  and  there  is 
formed  as  a  maximum  about  0.9  per  cent,  of  lactic 
acid.  More  acid  may  be  formed  after  some  time. 
Hence,  sour  milk,  when  two  or  three  days  old,  con- 
tains only  3.5  to  4  per  cent,  of  milk-sugar.  The  sugar 
of  milk  passes  largely  into  the  whey  in  cheese-making 
and  forms  over  70  per  cent,  of  the  solids  in  whey. 
The  milk-sugar  of  commerce  is  usually  prepared  by 
evaporating  whey  and  purifying  the  impure  product 
first  obtained. 

THE  SALTS  OF  MILK 

The  salts  of  milk,  commonly  included  under  the 
term  "ash,"  are  present  in  only  small  amounts,  0.7 
per  cent,  on  the  average ;  but  they  have  important 
relations  to  milk  and  its  products.  Our  knowledge  of 
these  compounds  is  very  incomplete.  The  salts  of  milk 
are  commonly  spoken  of  as  the  ash  or  mineral  constitu- 
ents. This  conception  is  somewhat  misleading,  be- 
cause the  materials  appearing  in  the  ash  of  milk  are, 
to  some  considerable  extent,  combined  in  organic  com- 
pounds, instead  of  existing  in  the  milk  as  separate 


14  MODERN    METHODS    OF   TESTING    MILK 

inorganic  bodies.  The  ash  represents  in  amount, 
therefore,  more  than  the  so-called  mineral  constitu- 
ents of  milk  and  less  than  the  salts  of  milk.  While 
the  ash  in  milk  amounts  to  about  0.7  per  cent.,  the 
amount  of  salts  probably  approximates  0.9  per  cent. 
A  portion  of  the  salts  of  milk  is  in  solution,  including 
such  compounds  as  calcium  citrate,  sodium  chloride, 
potassium  acid  phosphate,  etc.,  while  a  portion  (tri- 
calcium  phosphate)  appears  to  be  in  suspension  in 
the  form  of  very  finely  divided  particles. 

THE  GASES  OF  MILK 

Milk  contains  more  or  less  oxygen  and  nitrogen, 
these  gases  being  carried  into  it  mechanically  from 
the  air  in  the  process  of  milking.  It  contains  also, 
when  freshly  drawn,  carbon  dioxide,  already  present 
in  the  udder  milk,  there  being  probably  between  3  and 
4  per  cent,  by  volume,  a  portion  of  which  escapes,  at 
once  while  being  drawn  from  the  udder  under  usual 
conditions. 

GENERAL  SUMMARY 

Milk  contains  water,  fat,  casein,  albumin,  sugar, 
salts,  carbon  dioxide  and  some  other  constituents  in 
small  quantities.  The  fat  and  casein  and  some  of  the 
salts  are  in  suspension  and  not  in  solution,  while  al- 
bumin, sugar  and  the  larger  portion  of  the  salts  are 
held  in  solution  by  the  water. 

As  a  matter  of  convenience,  the  compounds  of  milk 
are  divided  into  certain  arbitrary  groups.  By  one 
system  of  division,  the  compounds  of  milk  are  ar- 
ranged in  two  classes: — (i)  Water,  and  (2)  milk- 
solids  (or  total  solids),  this  second  class  including 


CHEMISTRY    OF    COWS     MILK 


fat,  casein,  albumin,  sugar,  salts  (ash),  etc.  Another 
division  is  made  on  the  basis  of  the  milk-fat  into  (i) 
fat  and  (2)  milk-scrum,  which  includes  all  the  milk 
constituents  except  the  fat  Separator  skim-milk  is 
nearly  pure  milk-serum.  Then  we  have  the  milk- 
solids  subdivided  into  (i)  fat  and  (2)  solids-not-fat 
(casein,  albumin,  sugar,  salts  (ash),  etc.) 

The  following  arrangement  shows  the  general  rela- 
tion of  the  compounds  contained  in  milk,  the  figures 
indicating  the  percentages  present  in  average  milk: 


MILK.    • 


Water 
87.1 


Solids 
12.9 


Fat  f  Nitrogen 

3.9  compounds 

3.2 
Solids-not-fat    I 

9.0  1  Milk-sugar 

5.1 

Ash  (salts) 
[  0.7 

!  Carbon  dioxide 
Nitrogen 
Oxygen 

AVERAGE  ANALYSIS   OF  COWS'   MILK 


f       Casein, 
2.5 

I  Albumin,  etc. 
0.7 


WATER 

TOTAL 
SOLIDS 

FAT 

CASEIN 

ALBU- 
MIN 

SUGAR 

ASH 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Per  ct. 

Average  of  5,552 

American   an- 

alyses    c  o  ni- 
pped    by    the 

author  .... 

87.1 

12.9 

3.9 

2.5 

0.7 

5.1 

0.7 

Average  cheese- 

factory  milk 

for  the  season 

(May  to  Nov.) 
inN.Y.  State... 

87.4 

12.6 

3.75 

2.45 

0.7 

5.0 

0.7 

l6  MODERN    METHODS    OF   TESTING    MILK 

REPRESENTATIVE  ANALYSES  OF  PRODUCTS  AND  BY-PRODUCTS  OF  MILK 


WATER 

TOTAL 
SOLIDS 

FAT 

CASEIN 

ALBU- 
MIN 

SUGAR 

ASH 

Butter 

Per  ct. 
13  0 

Per  ct. 
87.0 

Per  ct. 
83  5 

Per  cl. 

1.0 

Per  ct. 

Per  ct. 

Per  ct. 

2  5  i 

Cheddar  Cheese 
(green) 
Skim-milk 
(separator) 

Whey  

36.8 
90.3 
93  4 

63.2 
9.7 
6  6 

33.75 

0.10 
0  35 

23.752 
2.75 
0.10 

o.eo 

0  75 

5.25 
4  80 

5.73 
0.80 
0  60 

Buttermilk  

90  6 

9.4 

0  10 

2.80 

0.80 

4  40* 

0  70 

.    2  Paracasein.    3  Salt  and  Ash.    *. 60  per  cent,  lactic  acid  in  addition. 

DEFINITIONS   AND   STANDARDS    OF   MILK   AND 
MILK    PRODUCTS 

The  United  States  Department  of  Agriculture  has 
established  official  standards  for  purity  of  dairy  and 
other  food  products,  defining  also  what  is  meant  by  the 
terms  used  in  designating  different  materials.  These 
definitions  and  standards  have  been  most  carefully 
worked  out  by  members  of  the  Association  of  Official 
Agricultural  Chemists,  several  years  having  been  de- 
voted to  the  collection  of  data.  The  official  definitions 
and  standards  relating  to  milk  and  milk  products  are 
as  follows: 

MILK 

Definitions. — i.  Milk  (whole  milk)  is  the  lacteal 
secretion  obtained  by  the  complete  milking  of  one 
or  more  healthy  cows,  properly  fed  and  kept,  exclud- 
ing that  obtained  within  fifteen  days  before  and  five 
days  after  calving. 

2.  Blended  milk  is  milk  modified  in  its  composition 


CHEMISTRYOT      OWS'    MILK  17 


so  as  to  have  a  definite  and  stated  percentage  of  one 
or  more  of  its  constituents. 

3.  Skim-milk  is  milk  from  which  a  part  or  all  of 
the  cream  has  been  removed. 

4.  Buttermilk  is  the  product  that  remains  when  but- 
ter is  removed  from  milk  or  cream  in  the  process  of 
churning. 

5.  Pasteurized  milk   is  milk  that  has   been  heated 
below  boiling  but  sufficiently  to  kill  most  of  the  act- 
ive organisms  present  and  immediately  cooled  to  fifty 
degrees   (50°)   Fahr.  or  lower  to  retard  the  develop- 
ment of  their  spores. 

6.  Sterilized  milk  is  milk  that  has  been  heated  at 
the  temperature  of  boiling  water  or  higher  for  a  length 
of  time  sufficient  to  kill  all  organisms  present. 

7.  Condensed  milk  is  milk  from  which  a  considera- 
ble portion  of  water  has  been  evaporated. 

8.  Sweetened  condensed  milk  is  milk  from  which 
a  considerable  portion  of  water  has  been  evaporated 
and  to  which  sugar  (sucrose)  has  been  added. 

9.  Condensed  skim-milk   is   skim-milk   from   which 
a  considerable  portion  of  water  has  been  evaporated. 

Standards.  —  I.  Standard  milk  contains  not  less  than 
twelve  (12)  per  cent,  of  total  solids,  not  less  than  eight 
and  one-half  (8.5)  per  cent,  of  solids-not-fat,  and  not 
less  than  three  and  one-quarter  (3.25)  per  cent,  of 
milk-  fat. 

2.  Standard  skim-milk  contains  not  less  than  nine 
and  one-quarter  (9.25)  per  cent,  of  milk-solids. 

3.  Standard  condensed  milk  contains  not  less  than 
twenty-eight   (28)    per  cent,  of  milk-solids,  of  which 
not  less  than  one-  fourth  is  milk-  fat. 


18  MODERN    METHODS    OF   TESTING    MILK 

4.  Standard  sweetened  condensed  milk  contains  not 
less  than  twenty-eight  (28)  per  cent,  of  milk-solids  of 
which  not  less  than  one-fourth  is  milk-fat. 

MILK-FAT  OR  BUTTER-FAT 

Definition.  —  Milk-fat  or  butter-fat  is  the  fat  of 
milk. 

Standard.  —  Standard  milk-fat  or  butter-fat  has  a 
Reichert-Meissl  number  not  less  than  twenty-  four  (24) 
and  a  specific  gravity  not  less  than  0.905 


CREAM 

Definitions.  —  i.  Cream  is  that  portion  of  milk,  rich 
in  butter-fat,  which  rises  to  the  surface  of  milk  on 
standing,  or  is  separated  from  it  by  centrifugal  force. 

2.  Evaporated  cream  is  cream  from  which  a  consid- 
erable portion  of  water  has  been  evaporated. 

Standard.  —  Standard  cream  contains  not  less  than 
eighteen  (18)  per  cent,  of  milk-  fat. 

BUTTER 

Definitions.  —  I.  Butter  is  the  product  made  by 
gathering  in  any  manner  the  fat  of  fresh  or  ripened 
milk  or  cream  into  a  mass,  which  also  contains  a  small 
portion  of  the  other  milk  constituents,  with  or  with- 
out salt. 

2.  Renovated  or  process  butter  is  the  product  made 
by  melting  butter  and  reworking,  without  the  addition 
or  use  of  chemicals  or  any  substances  except  milk, 
cream  or  salt. 

Standards.  —  i.  Standard  butter  contains  not  less 
than  eighty-two  and  five-tenths  (82.5)  per  cent,  of 


CHEMISTRY    OF    COWS     MILK  19 

butter-fat.  By  acts  of  Congress  approved  August 
2,  1886,  and  May  9,  1902,  butter  may  also  contain 
additional  coloring  matter. 

2.  Standard  renovated  or  process  butter  contains  not 
more  than  sixteen  (16)  per  cent,  of  water  and  at  least 
eighty-two  and  five-tenths  (82.5)  per  cent,  of  but- 
ter-fat. 

CHEESE 

Definitions. — i.  Cheese  is  the  solid  and  ripened  pro- 
duct made  by  coagulating  the  casein  of  milk  by  means 
of  rennet  or  acids,  with  or  without  the  addition  of 
ripening  ferments  and  seasoning.  By  act  of  Congress, 
approved  June  6,  1896,  cheese  may  also  contain  addi- 
tional coloring  matter. 

2.  Whole-milk  or  full-cream  cheese  is  cheese  made 
from  milk  from  which  no  portion  of  the  fat  has  been 
removed. 

3.  Skim-milk  cheese  is  cheese  made  from  milk  from 
which  any  portion  of  the  fat  has  been  removed. 

4.  Cream-cheese    is    cheese    made    from    milk    and 
cream,  or  milk  containing  not  less  than  six   (6)   per 
cent,  of  fat. 

Standard. — Standard  whole-milk  or  full-cream 
cheese  contains,  in  the  water-free  substance,  not  less 
than  fifty  (50)  per  cent,  butter-fat. 

MISCELLANEOUS   MILK  PRODUCTS 
Definitions. — 1.  Whey  is  the  product  remaining  af- 
ter the  removal  of  fat  and  casein  from  milk  in  the  pro- 
cess of  cheese-making. 

2.  Kumiss  is  the  product  made  by  the  alcoholic  fer- 
mentation of  mares'  or  cows'  milk,  with  or  without  the 
addition  of  sugar  (sucrose). 


CHAPTER    II 

Methods  of  Sampling  Milk 

Too  much  emphasis  can  not  be  placed  upon  the  im- 
portance of  taking  for  analysis  a  sample  of  milk  that 
truly  represents  the  whole  body  of  milk  from  which 
the  sample  is  taken.  This  statement  applies  equally 
to  any  product  or  by-product  of  milk  that  is  to  be 
tested.  Before  a  sample  for  testing  is  taken,  the  body 
of  milk  from  which  the  sample  is  to  be  drawn  should 
be  uniform  throughout  in  composition.  Several  con- 
ditions may  disturb  the  desired  uniformity  of  compo- 
sition of  a  mass .  of  milk,  among  which  are  the  fol- 
lowing : 

(1)  Separation  of  fat. 

(2)  Partial  churning  of  fat. 

(3)  Freezing  of  milk. 

(4)  Souring  ofjnilk. 

SAMPLING  MILK  WHEN   FAT   HAS   SEPARATED 

The  rapidity  with  which  fat-globules  rise  to  the 
surface  of  milk  in  the  form  of  cream  is  well  known. 
Therefore,  milk  standing  at  rest  soon  loses  its  uni- 
formity of  composition,  the  upper  layers  containing 
more  fat  than  the  lower  ones.  On  this  account  it  is 
always  necessary,  just  before  taking  a  sample  of 
milk  for  testing,  to  make  sure  that  the  body  of  milk 
to  be  tested  has  an  even  composition  throughout. 

Milk  in  which  fat  separation  is  slight. — In  milk 

20 


METHODS   OF   SAMPLING    MILK  2I 

in  which  there  is  no  visible  separation  of  cream,  even- 
ness of  mixing  may  be  best  effected  by  pouring  the 
milk  from  one  vessel  to  another  several  times  immedi- 
ately before  each  sample  is  drawn  for  testing.  Stir- 
ring milk,  as  with  a  dipper,  is  less  effective  than 
pouring. 

Milk  in  which  fat  separation  is  marked. — In  milk 
in  which  the  cream  has  separated  in  a  visible  layer, 
the  pouring  needs  to  be  done  a  greater  number  of 
times  than  in  cases  where  the  separation  of  cream  is 
not  noticeable ;  and,  in  order  to  prevent  possible  churn- 
ing of  particles  of  cream,  the  agitation  should  be  as 
gentle  as  may  be  consistent  with  thorough  mixing. 

Milk  containing  dried  cream. — In  cases  where  the 
cream  is  somewhat  dried  or  hardened,  the  milk  should 
be  warmed  to  105°  or  110°  F.  for  5  or  10  minutes 
to  allow  the  cream  to  melt.  The  milk  is  then  vigor- 
ously agitated  and  immediately  sampled. 

SAMPLING  MILK  WHEN  FAT  IS  PARTIALLY 
CHURNED 

Milk- fat  may  separate  from  milk  in  the  form  of 
small  butter-granules,  as  (i)  when  the  mixing  or 
shaking  of  the  sample  to  be  tested  is  done  too  vio- 
lently; (2)  when  milk  in  cans  is  excessively  agitated 
in  transportation;  and  (3)  when  bottles,  partly  full 
of  milk,  are  sent  by  mail  or  express.  In  such  partially 
churned  milk  it  is  difficult  to  get  a  representative 
sample,  and  the  results  of  testing  are,  at  best,  only 
approximate,  unless  special  measures  are  resorted  to 
in  sampling. 

Distributing  fat  by  warming. — In  the  case  of  par- 


MODERN    METHODS   OF   TESTING   MILK 

tially  churned  milk,  the  fat  may  be  redistributed  in 
the  milk  by  warming  it  to  105°  or  110°  F.  long  enough 
to  melt  the  butter-granules,  after  which  the  sample 
is  vigorously  shaken,  until  the  fat  is  evenly  distributed 
through  the  milk,  and  then  the  sample  is  drawn  at 
once  for  analysis. 

Dissolving  fat  in  ether. — Another  method  of  treat- 
ing partially  churned  milk,  previous  to  sampling,  is 
to  shake  the  milk  with  5  per  cent,  of  its  volume  of 
ether  until  the  fat-granules  are  redissolved  and  then, 
after  further  vigorous  shaking,  to  take  the  sample  at 
once.  In  this  case  it  is  necessary  to  make  a  correc- 
tion by  adding  to  the  results  5,  per  cent,  or  one-twenti- 
eth of  the  result  obtained.  For  example,  a  milk, 
treated  with  5  per  cent,  of  ether,  and  giving,  on  test- 
ing, 3  per  cent,  of  fat,  should  have  added  .15  (5  per 
cent,  of  3),  making  the  corrected  result  3.15  per  cent. 
When  ether  is  used,  extra  care  must  be  observed  in 
mixing  the  acid  and  milk,  (see  p.  58)  as  the  heat  de- 
veloped may  cause  the  ether  to  boil  up  out  of  the 
neck  of  the  test-bottle. 

Measures  for  preventing  the  churning  of  fat  in 
milk. — It  is  better  to  prevent  the  churning  of  fat  in 
milk  than  to  be  put  to  the  extra  trouble  required  to 
get  a  good  sample  from  milk  that  has  in  it  fat-granules. 
Cans  of  milk,  when  necessarily  exposed  to  much  mo- 
tion in  transportation,  should  be  made  as  nearly  full 
as  possible.  In  the  case  of  bottles  of  milk  sent  by 
mail  or  express  for  analysis,  the  churning  of  fat  may 
be  prevented  in  the  following  manner:  Fill  the  bot- 
tle full  of  milk  to  overflowing.  Then  push  in  tightly 
a  stopper  of  cork  or  rubber  in  which  has  been  made 


METHODS   OF   SAMPLING   MILK  23 

from  top  to  bottom  a  hole  one-eighth  inch  in  diameter 
or  less.  Finally,  push  a  close-fitting  plug  of  wood  or 
a  glass  rod  into  the  hole  in  the  stopper. 

SAMPLING  FROZEN  MILK 

Frozen  milk  is  of  very  uneven  composition  in  dif- 
ferent portions  of  its  mass.  The  crystals  of  ice  con- 
tained in  it  consist  largely  of  water,  while  the  liquid 
portion  contains  most  of  the  milk-solids.  In  such 
cases  it  is  necessary  to  melt  the  frozen  portion  by 
warming,  and  then  to  mix  well  by  gentle  pouring 
from  one  vessel  to  another,  after  which  the  sample  is 
at  once  taken  for  testing. 

SAMPLING  MILK  COAGULATED  BY  SOURING 

A  sample  of  thickened,  sour  milk  can  not,  without 
special  treatment,  be  taken  so  as  to  give  reliable  results 
in  fat  determination.  In  ordinary  curdled  milk  the 
percentage  of  fat  remains  unchanged  in  amount,  but 
it  is  not  evenly  distributed  through  the  milk.  In  or- 
der to  overcome  this  difficulty,  the  curdled  casein 
lactate  must  be  dissolved  before  sampling.  This  is 
done  by  adding  to  the  milk  a  strong  solution  of  caus- 
tic soda  or  potash  (lye),  or  strong  ammonia  water, 
to  the  extent  of  5  or  10  per  cent,  of  the  volume  of  the 
milk  used  for  sampling.  The  alkali  is  shaken  with 
the  milk  until  the  mixture  becomes  completely  liquid, 
after  which  the  sample  is  at  once  drawn  for  testing. 
It  is  necessary  to  make  a  correction  by  adding  to  the 
results  5  or  10  per  cent,  of  the  amount  of  fat  found, 
according  to  the  amount  of  alkali  solution  used.  In 
place  of  using  a  solution  of  alkali,  one  can  add,  in 


24  MODERN    METHODS   OF   TESTING    MILK 

small  portions  at  a  time,  finely  powdered  caustic  soda 
or  potash,  allowing  the  milk  to  stand  some  time  after 
each  addition  of  powdered  alkali  and  shaking  vigor- 
ously, the  additions  of  alkali  and  the  agitation  being 
continued  only  until  the  milk  becomes  completely  liquid. 
In  using  the  alkali  in  solid  form,  no  correction  of  re- 
sults needs  to  be  made.  The  alkali  solution  or  tab- 
lets described  on  page  96  may  be  used.  A  darkening 
of  the  milk  by  alkali  may  occur  without  affecting  the 
results  of  the  test.  In  testing,  caution  must  be  ob- 
served when  adding  sulphuric  acid  (see  p.  56)  to  milk 
in  which  an  alkali  has  been  used,  since  an  unusual  de- 
gree of  heat  is  produced  and  the  contents  of  the  test- 
bottle  may  spurt  out.  The  acid  must  be  added  slowly 
and  mixed  with  the  milk  much  more  deliberately  than 
usual. 

COMPOSITE  SAMPLING  OF  MILK 

Composite  samples  of  milk. — A  mixture  of  daily 
samples  of  milk,  taken  from  day  to  day  for  several 
days  in  succession,  is  known  as  a  composite  sample. 
In  commercial  work  at  creameries,  cheese-factories, 
milk-shipping  stations,  etc.,  where  the  number  of  pa- 
trons is  large,  a  daily  test  of  the  milk  for  its  fat  con- 
tent is  impracticable.  To  obviate  the  great  amount  of 
work  involved  in  making  daily  tests,  a  jar  is  provided 
for  the  milk  of  each  patron  and  in  this  jar  is  placed 
a  sample  of  each  day's  milk,  when  it  is  delivered,  these 
daily  samples  being  mixed  and  allowed  to  accumulate 
for  a  period  of  one  or  two  weeks.  A  determination 
of  fat  in  such  a  composite  sample  gives  the  average 
percentage  of  fat  in  the  milk  for  the  period  covered 


METHODS    OF    SAMPLING    MILK 


by  the  mixture  of  daily  samples.  This  method  has 
been  proved  to  be  as  accurate  as  that  of  testing  each 
sample  daily  by  itself,  but  there  are  several  precau- 
tions to  be  observed  carefully  in  applying  this  method 
in  commercial  practice. 

The  conditions  that  are  necessary  for  success  in 
using  the  method  of  composite  sampling  may  be  con- 
sidered under  the  following  heads:  (i)  Systematic 


FIG.    I 
COMPOSITE- SAMPLE   JAR 


FIG.    2 
COMPOSITE-SAMPLE  JAR 


preparation,  (2)  methods  of  taking  daily  samples,  (3) 
use  of  preservatives,  (4)  care  of  composite  samples, 
(5)  a&e  °f  composite  samples,  and  (6)  preparation  of 
composite  samples  for  sampling  and  testing. 

Systematic  preparation  for  taking  composite  sam- 
ples.— A  round  glass  jar  or  bottle,  holding  a  pint  or 
quart,  should  be  provided  for  each  patron.  The  forms 
given  in  Figs.  I  and  2  are  suitable,  or  ordinary  Mason 


26  MODERN    METHODS   OF   TESTING    MILK 

fruit-jars  may  be  used.  Whatever  form  of  composite- 
sample  jar  or  bottle  be  used,  .the  stopper  or  cover 
should  fit  perfectly  tight,  so  as  to  prevent  any  possi- 
ble evaporation  of  water  from  the  sample  of  milk, 

and  care  should  be 
taken  to  keep  the 
covers  or  stoppers 
tight.  Each  sam- 
ple-bottle or  jar 
should  be  labeled 
with  a  name  or 
number  easily  iden- 
tifying the  patron 
furnishing  the  milk. 
The  jars  should  be 
arranged  in  definite 
order  on  a  rack 

FIG.    3 — RACK    FOR    COMPOSITE    SAMPLES 

(Fig.  3),  placed 

conveniently  near  the  point  where  the  milk  is  deliv- 
ered. As  explained  later,  some  preservative  is  used 
in  each  jar. 

Taking  daily  samples  for  composite  samples. — 
Each  day  when  milk  is  delivered,  the  sample  should 
be  taken  immediately  after  the  milk  has  been  poured 
into  the  weighing  can  before  weighing,  and  should 
then  be  placed  at  once  in  the  composite  jar  or  bottle 
prepared  for  it.  Two  methods  of  sampling  are  in 
common  use,  (i)  by  means  of  a  small  dipper,  and  (2) 
by  means  of  a  sampling-tube. 

(i)  Taking  sample  with  dipper, — A  half-ounce  dip- 
per (Fig.  4)  is  used  for  taking  the  sample  from  the 
weigh-can,  as  soon  as  the  milk  is  poured  in.  The 


METHODS    OF    SAMPLING    MILK  27 

sample  is  at  once  placed  in  its  proper  jar  or  bottle. 
Providing  the  milk  is  thoroughly  mixed  in  the  weigh- 
can  and  the  quantity  of  milk  delivered  by  a  patron 


FIG.   4 
SAMPLING-DIPPER 


FIG.    5 
SCOViiLL  SAMPLER 


FIG.    6 
EQUITY    SAMPLER 


from  day  to  day  does  not  vary  much,  this  method  of 
sampling  gives  correct  results. 

(2)  Taking  sample  with  sampling-tube. — There  are 
different  types  of  sampling-tubes  (Figs.  5  and  6),  of, 
which  the  Scovell  sampler  is  one  of  the  best.  In  this 


28  MODERN    METHODS   OF   TESTING    MILK 

instrument  the  main  tube  is  open  at  both  ends,  the 
lower  end  closely  fitting  into  a  cap  furnished  with 
three  elliptical  openings.  When  the  sampler,  open  at 
the  bottom,  is  let  down  into  a  can  of  milk,  the  liquid 
pours  into  the  openings  arid  fills  the  tube  to  the  height 
of  the  milk  in  the  can.  When  the  cap  comes  in  con- 
tact with  the  bottom  of  the  can,  the  tube  slides  down 
and  closes  the  openings,  after  which  the  tube  can  be 
withdrawn  and  its  contents  emptied  into  the  com- 
posite jar. 

The  tube  method  of  sampling  possesses  two  marked 
advantages  over  the  dipper  method :  ( i )  It  always 
takes  an  aliquot  portion,  or  uniform  proportion,  of 
the  milk,  representing  a  small  column  of  the  milk 
from  top  to  bottom ;  and  (2)  it  provides  a  strictly  rep- 
resentative sample  of  the  milk,  even  when  sampling 
is  delayed,  because  it  takes  a  uniform  amount  from 
each  layer  of  milk,  going  from  top  to  bottom. 

THE    USE    OF    PRESERVATIVES    IN    COMPOSITE 
SAMPLES 

The  successful  use  of  composite  samples  is  made 
possible  only  by  the  presence  of  some  substance  which 
will  keep  the  milk  from  curdling.  Three  preserva- 
tives have  been  found  especially  useful  for  this  pur- 
pose: (i)  Corrosive  sublimate,  (2)  formalin,  and 
(3)  bichromate  of  potash. 

Corrosive  sublimate,  known  chemically  as  mercuric 
chloride,  has  the  advantage  of  being  a  more  powerful 
antiseptic  than  the  other  substances,  much  smaller 
quantities  being  effective  in  keeping  milk  longer,  but 
it  has  the  disadvantage  cf  being  a  violent  poison. 


METHODS   OF    SAMPLING    MILK  2Q 

When  this  is  used  as  a  milk  preservative,  it  is  a  wise 
precaution  to  add  a  little  coloring  matter  to  the  milk 
in  order  to  warn  every  one  of  its  abnormal  character. 
Corrosive  sublimate,  mixed  with  coloring  matter,  is 
put  up  in  convenient  tablet  form  and  has  found  exten- 
sive use  in  preserving  composite  samples.  All  things 
considered,  it  is  probably  the  most  satisfactory  of  the 
preservatives  commonly  employed. 

Formalin  is  a  liquid  containing  about  40  per  cent, 
of  the  chemical  compound  known  as  formaldehyde.  It 
is  an  effective  antiseptic  and  has  the  advantage  of 
being  in  liquid  form.  One  cubic  centimeter  of  forma- 
lin should  keep  a  pint  or  quart  sample  of  milk  two 
weeks  or  more.  Formalin  possesses  the  disadvantage 
of  so  hardening  the  milk-casein  that  it  is  not  as  readily 
dissolved  by  sulphuric  acid  (see  p.  58)  as  is  the  casein 
of  untreated  milk.  An  excessive  use  of  corrosive  sub- 
limate may  produce  a  similar  hardening  of  casein. 

Bichromate  of  potash,  also  called  potassium  bichro- 
mate, is  extensively  used  in  preserving  samples  of 
milk  for  testing.  It  is  best  to  use  it  in  powdered  form. 
It  has  the  following  advantages:  (i)  It  is  compara- 
tively inexpensive.  (2)  It  colors  milk  yellow  and  thus 
shows  its  presence.  (3)  It  is  not  a  very  violent  poison, 
though  not  entirely  harmless.  (4)  It  is  efficient  in 
keeping  milk  for  one  or  two  weeks.  However,  it  has 
some  disadvantages  as  a  preservative  of  composite 
samples  of  milk:  (i)  If  too  much  bichromate  is  used, 
the  solution  of  the  casein  in  sulphuric  acid  is  some- 
what difficult  and  the  final  results  of  testing  may  not 
be  clear.  (2)  In  hot  weather,  it  is  often  difficult  to 
keep  samples  without  using  an  excessive  amount  of 


3O  MODERN    METHODS   OF  TESTING   MILK 

bichromate.  (3)  Lactic  acid  in  milk  considerably  re- 
duces the  efficiency  of  bichromate  in  preserving  milk. 
(4)  Samples  of  milk  preserved  with  bichromate  are 
apt,  when  exposed  to  light,  to  form  a  tough  skin  on 
the  surface,  which  interferes  with  proper  sampling. 

The  amount  of  potassium  bichromate  to  be  used  in 
composite  samples  is  about  8  or  10  grains  for  half  a 
pint  to  a  pint  of  milk.  The  bichromate  is  put  up  for 
sale  in  tablets  of  convenient  size,  ready  for  use  in  pre- 
serving milk  samples.  Bichromate  can  be  satisfactor- 
ily used  even  in  hot  weather,  if  the  samples  are  kept 
in  a  dark,  cool  place  most  of  the  time. 

CARE  OF  COMPOSITE  SAMPLES 

In  caring  for  composite  samples  of  milk  or  cream, 
some  special  precautions  must  be  observed,  (i)  Com- 
posite sample  jars  must  be  kept  covered  tight  to  pre- 
vent evaporation  of  water,  which  would  result  in  giv- 
ing a  test  for  fat  higher  than  the  correct  amount.  (2) 
They  should  be  kept  in  a  cool  place,  so  that  the  small- 
est possible  amount  of  preservative  will  need  to 
be  used.  (3)  They  should  be  kept  in  the  dark 
most  of  the  time,  since  direct  sunlight  may  cause 
the  formation  of  a  tough  cream,  rendering  difficult 
the  taking  of  a  good  sample  for  testing.  (4)  When 
the  daily  sample  of  milk  is  added  to  the  composite 
sample,  the  contents  of  the  jar  should  be  mixed  by 
giving  the  jar  a  gentle,  rotary  motion.  Unless  this 
is  done  regularly  each  day,  the  cream  that  rises  be- 
comes tough,  especially  where  it  is  in  contact  with  the 
sides  of  the  jar,  and  this  condition  makes  it  difficult 
to  get  a  proper  sample  for  testing.  This  daily  mixing 


METHODS    OF    SAMPLING    MILK  3! 

also  insures  the  complete  solution  and  distribution  of 
the  preservative  through  the  milk,  which  is  an  es- 
sential condition  of  success  in  keeping  samples.  (5) 
If  a  composite  sample  shows  any  dried  or  churned 
cream,  the  sample  should  be  warmed  to  105°  or  110°  F. 
for  some  minutes  and  then  agitated  vigorously  be- 
fore drawing  the  sample  for  testing. 

AGE   OF   COMPOSITE   SAMPLES   WHEN   TESTED 

It  is  advisable  to  make  the  fat-test  in  composite 
samples,  when  they  have  been  accumulating  for  a 
week  or  ten  days.  In  any  case  the  limit  should  be 
placed  at  two  weeks.  The  custom  practiced  by  some 
of  testing  composite  samples  only  once  a  month  should 
be  severely  condemned.  When  samples  are  kept  longer 
than  two  weeks,  it  is  more  difficult  to  get  a  perfectly 
reliable  test  for  fat. 

PREPARATION    OF    COMPOSITE    SAMPLES    FOR 
SAMPLING  AND  TESTING 

When  a  composite  sample  is  to  be  tested,  it  is 
treated  like  any  other  sample  previous  to  taking  the 
sample  for  testing,  as  has  already  been  described  in 
the  first  part  of  this  chapter  on  pp.  20-24. 


CHAPTER    III 

The  Babcock  Test— Description  of  Apparatus 
and  Material 

The  Babcock  test  is  a  method  for  ascertaining  the 
amount  of  fat  in  milk  and  milk  products.  It  was  de- 
vised by  S.  M.  Babcock,  Ph.D.,  chief  chemist  of  the 
Wisconsin  Agricultural  Experiment  Station,  and  was 
first  made  public  in  1890.  There  are  in  use,  espe- 
cially in  Europe,  other  tests,  which  are  more  or  less 
imitations  or  modifications  of  the  Babcock  test,  such 
as  the  Gerber  test  or  acid-butyrometer  and  DeLaval's 
butyrometer. 

The  Babcock  test  solved  the  problem  of  a  rapid,  ac- 
curate, inexpensive  and  simple  method  of  testing  milk 
and  milk  products  for  fat,  and  it  has  found  extensive 
application  in  many  lines  of  dairying,  as  may  be  shown 
by  mention  of  the  following  important  results  coming 
from  its  use :  ( i )  The  payment  for  milk  according  to 
its  fat  content  has  been  made  practicable.  (2)  Mak- 
ers of  butter  and  cheese  have  been  able  to  detect  and 
prevent  abnormal  losses  of  fat  in  the  process  of  man- 
ufacture. (3)  It  has  enabled  milk  producers  to  detect 
unprofitable  cows,  thus  furnishing  an  intelligent  guide 
in  improving  their  herds.  (4)  It  has  done  more  than 
any  other  means  to  stop  the  watering  and  skimming  of 
milk  in  connection  with  creameries  and  cheese- factor- 
ies. (5)  It  has  been  of  great  service  in  scientific  dairy 
investigations  and  has,  in  general,  been  a  source  of 
educational  inspiration. 

32 


THE    BABCOCK    TEST  33 

PRINCIPLES  AT  BASIS  OF  BABCOCK  TEST 

This  method  is  based  on  the  action  of  two  agents: 
(i)  the  action  of  strong  sulphuric  acid  upon  the  con- 
stituents of  milk-serum,  and  (2)  the  action  of  cen- 
trifugal force. 

Action  of  sulphuric  acid  in  Babcock  test. — The  sul- 
phuric acid  used  in  the  Babcock  test  performs,  at  least, 
three  functions,  which  we  will  consider  briefly. 

(1)  Action  on  serum-solids  of  milk. — Strong  sul- 
phuric acid  acts  chemically  and  physically  upon  the 
milk-serum  solids   (casein,  sugar,  albumin  and  salts) 
in  such  a  way  as  to  destroy  that  strong  mechanical,  ad- 
hesive   influence    exerted    by   the   milk-serum    solids, 
which   tends   to   prevent   the    fat-globules    separating 
from  the  form  of  an  emulsion.    When  this  influence  is 
overcome,  the  fat-globules  are  more  free  to  collect  in 
a  mass. 

(2)  Heat  furnished  by  action  of  sulphuric  acid. — 
The  action  of  sulphuric  acid  upon  the  water  of  milk- 
serum  and  also  upon  the  organic  solids  of  the  serum 
generates  so  much  heat  that  the  fat-globules  easily  lose 
their  individuality  and  run  together,  a  condition  favor- 
ing rapid  separation  of  fat  from  serum. 

(3)  Specific  gravity  of  serum  increased  by  sulphuric 
acid. — The  sulphuric  acid,  being  nearly  twice  as  heavy 
as  milk,  increases  the  difference  Jn  specific  gravity  be- 
tween the  milk-fat  and  the  liquid  surrounding  it.    The 
milk-fat,  being  much  lighter,  more  readily  rises  to  the 
surface  of  the  heavy  liquid. 

Action  of  centrifugal  force  in  Babcock  test. — The 
action  of  the  sulphuric  acid  having  released  the  milk- 
fat  largely  from  the  form  of  an  emulsion  in  the  milk- 


34 


MODERN    METHODS   OF   TESTING    MILK 


serum,  the  completion  of  the  separa- 
tion of  fat  is  effected  by  centrifugal 
force.  When  the  bottles  containing 
the  mixture  of  milk  and  acid  are 
whirled,  the  centrifugal  force  acts 
more  strongly  upon  the  heavier  por- 
tion, that  is,  the  mixture  of  acid  and 
milk-serum.  Hence  this  heavy  mix- 
ture is  forced  to  the  outside,  which  is 
the  bottom  of  the  bottle,  while  the 
much  lighter  fat  is  forced  to  the  top. 
A  small  amount  of  fat  (.1  to  .2  per 
cent.)  remains  unseparated  under 
usual  conditions. 

The  following  apparatus  and  ma- 
terial are  used  in  making  the  test :  ( i ) 
Test-bottles,  (2)  pipette  for  measur- 
ing milk,  (3)  acid-measure,  (4)  tes- 
ter or  centrifugal  machine,  and  (5) 
sulphuric  acid. 

TEST-BOTTLES 

The  usual  form  of  bottle  used  in 
testing  milk  is  shown  in  Fig.  7.  The 
neck  of  the  bottle  is  marked  with  a 
scale  so  graduated  that  each  small  di- 
vision represents  .2  per  cent,  and  five 
of  these  divisions,  making  one  large 
division,  represent  i  per  cent.,  when  we  use  17.50:.* 
or  18  grams  of  milk.  The  marks  extend  from  o  to  10 


FIG.    7 

MILK-TESTING 
BOTTLE 


*cc.  is  the  abbreviation  for  cubic  centimeters  (see  p.  205). 


THE   BABCOCK   TEST 


35 


176  c.c 


\/ 


per  cent.  Why  do  these  divisions  represent 
exact  percentages  by  weight  of  fat  in  milk, 
when  no  weighing  is  done  in  testing  milk? 
We  use,  in  testing,  17.5  cc.  of  milk,  which 
is  known  to  weigh  almost  exactly  18  grams. 
The  graduated  portion  of  the  neck  of  the 
test-bottle  is  made  to  hold  exactly  2  cc.  be- 
tween the  o  and  10  marks.  Since  i  cc.  of 
pure  milk-fat  is  known  to  weigh  .9  gram, 
2  cc.  of  milk- fat,  the  amount  required  to 
fill  the  neck  between  the  o  and  10  marks, 
weighs  1.8  (.9x2)  grams,  which  amount  is 
just  10  per  cent,  of  the  18  grams  of  milk 
sample  used  in  testing. 

The  divisions  on  the  neck  of  the  test-bot- 
tle should  be  accurate  and  uniform ;  the  lines 
should  run  straight  across  the  neck  and  not 
obliquely.  When  the  marks  and  numbers 
become  indistinct  from  use,  they  can  be 
rendered  clear  by  rubbing  the  scale  over 
with  the  lead  of  a  pencil  or  with  a  cloth 
having  on  it  a  little  printer's  ink  or  black 
paint.  When  in  use,  each  bottle  should  be 
numbered  or  labeled  in  a  distinctive  way. 


FIG.  8 

PIPETTE 


MILK-MEASURING  PIPETTE 

The  form  of  pipette  in  common  use  is 
shown  in  Fig.  8.  Other  forms  are  shown 
in  Figs.  9  and  10.  The  pipette  should  hold 
17.6  cc.  when  filled  to  the  mark.  Since 
about  .1  cc.  of  milk  will  adhere  to  the  in- 


30  MODERN    METHODS   OF  TESTING   MILK 

side,  such  a  pipette  will  furnish  a  sample  amounting  to 
17.5  cc.  of  milk,  which  weighs  about  18  grams,  I  cc. 
of  milk  weighing  about  1.03  grams  on  an  average. 
The  accuracy  of  the  test,  so  far  as  regards  the  amount 
of  sample  taken,  depends  upon  the  exactness  of  the  pi- 
pette in  holding  17.6  cc.  The  mark  on  the  stem  should, 
for  convenience,  be  two  inches  or  more  from  the  up- 
per end  of  the  pipette0 

MEASURE  FOR  ACID 

A  cylinder  of  glass,  like  that  shown 
in  Fig.  n,  with  a  lip  to  pour  from  and 
a  single  mark  at  17.5  cc.,  is  the  form 
commonly  used.  Other  forms  are  shown 
in  Figs.  12  and  13.  These  latter  forms, 
made  so  as  to  hold  enough  acid  for  20 


J 


FIG.   9 
AUTOMATIC   PIPETTE 


FIG.    10 

WAGNER'S  PIPETTE 


FIG.   II 
ACID-MEASURE 


THE    BABCOCK    TEST 


37 


or  more  tests,  are  probably  the  most  convenient  where 
many  samples  are  to  be  tested  at  the  same  time. 


FIG.    12 
ACID-BURETTE    AND    STAND 


FIG.    13 
AUTOMATIC    BURETTE 


THE    CENTRIFUGAL    MACHINE,    OR    TESTER 

The  centrifugal  machine  used  in  the  Babcock  test 
is  commonly  called  the  Babcock  tester.  Various  forms 
have  been  devised,  varying  in  size  from  those  adapted 
for  a  single  duplicate  test  up  to  the  needs  of  large  fac- 
tories. The  designs  of  recent  years  are  much  superior 
to  the  early  forms.  Some  of  the  different  types  are 


THE   BABCOCK    TEST  39, 

represented  in  Figs.  14,  15,  16  and  17.  In  general 
they  all  consist  of  a  revolving  disc  placed  in  a  hori- 
zontal position,  and  provided  with  swinging  pockets, 


FIG.    l6 — SMALL    HAND-TESTER 

in  which  the  test-bottles  are  placed.  When  at  rest, 
the  pockets  hang  down,  permitting  the  bottles  to 
stand  upright.  When  the  disc  is  in  motion  the  pock- 
ets swing  out,  carrying  the  bottles  to  a  horizontal  posi- 
tion, the  necks  of  the  bottles  being  directed  in  toward 
the  center.  The  testers  should  be  made  to  carry  an  even 
number  of  bottles.  The  steam-turbine  tester  is  the 
best  form  of  centrifugal  for  factory  work.  It  has  the 
advantage  of  maintaining  a  uniform  rate  of  speed 
and,  in  addition,  the  contents  of  the  bottles  are  kept 
hot,  and  hot  water  is  supplied.  In  some  forms,  in 
which  the  exhaust  steam  is  not  carried  away  and  in 


40  MODERN    METHODS   OF   TESTING   MILK 

which  no  dampers  are  provided  in  the  cover,  the  steam 
testers  may  heat  the  fat  too  high.  For  use  on  farms, 
hand-testers  are  available.  It  is  always  necessary  that 


FIG.    I/ — ELECTRIC   CENTRIFUGAL    MACHINE   OF   LATEST    DESIGN    FOR 
USE   IN   BABCOCK   TEST 

Capable  of  unusually  high  speed — safe,  accurate  and  convenient.     Made 
by   International    Instrument   Co.     Cambridge,    Mass. 

the  tester  should  be  securely  fastened  to  a  firm  founda- 
tion and  so  set  that  the  revolving  disc  is  level.  The 
centrifugal  should  run  smoothly,  without  jar  or  trem- 
ble, when  going  at  full  speed. 

Estimating  speed  of  centrifugal  tester. — In  order 
to  cause  separation  of  the  most  fat  possible,  the  cen- 
trifugal disc  must  move  at  a  sufficient  speed.  The  re- 
quired number  of  revolutions  depends  upon  the  diame- 
ter of  the  disc,  to  the  edge  of  which  the  test-bottles  are 


THE    BABCOCK   TEST  41 

attached.     The  smaller  the  wheel,  the  greater  must  be 
the  number  of  revolutions  a  minute. 

Farrington  and  Woll  have  prepared  the  following 
1:able,  showing  the  necessary  number  of  revolutions  for 
different  sizes  of  testers : 

DIAMETER  OF                                                      No.  of  revolutions 
WHEEL  IN  INCHES                                                of  disc  per  minute 
10 1074 

12 980 

14 909 

16 848 

18 800 

20 759 

22 724 

24 693 

In  the  case  of  steam-turbine  testers,  they  are,  or 
should  be,  made  to  run  at  the  desired  speed  under  a 
definite  head  of  steam.  These  testers  should  always 
be  provided  with  a  pressure-gage,  and  a  speed-indi- 
cator is  also  desirable. 

In  the  case  of  hand-testers,  the  speed  can  be  ascer- 
tained in  the  following  manner:  Give  the  handle  one 
full  turn  and  count  the  number  of  times  a  given  point 
on  the  disc  goes  round.  Suppose,  for  example,  that 
the  diameter  of  the  disc  is  16  inches  and  that  it  revolves 
14  times  for  one  turn  of  the  handle.  Such  a  disc  ought 
to  revolve  848  times  per  minute  according  to  the  pre- 
ceding table.  The  handle  must  be  turned  around  as 
many  times  a  minute  as  14  is  contained  in  848  in  or- 
der to  attain  the  desired  speed,  which  is  found  to  be 
about  60  times,  or  once  a  second.  Then,  with  watch 
in  hand,  regulate  the  turning  of  the  handle  until  it 


42  MODERN    METHODS    OF   TESTING    MILK 

is  made  to  turn  60  times  a  minute.  The  proper  speed 
once  attained  should  be  kept  up  during  the  testing  of 
a  sample.  The  efficiency  of  whirling  can  be  further 
tested  by  treating  different  samples  of  the  same  milk 
at  different  rates  of  speed,  the  highest  per  cent,  of 
fat  beyond  which  there  is  no  increase,  showing  the 
right  speed. 

KIND   OF  ACID  USED  IN  BABCOCK  TEST 

The  acid  used  in  the  Babcock  test  is  commercial  sul- 
phuric acid,  commonly  known  as  oil  of  vitriol.  It 
should  not  be  quite  as  strong  as  the  strongest  com- 
mercial acid.  While  the  strong  acid  has  a  specific 
gravity  of  about  1.84,  the  acid  used  in  the  test  should 
be  between  1.82  and  1.83  at  60°  F. 

Effect  of  weak  acid. — If  the  acid  is  weaker  than 
that  indicated  by  specific  gravity  1.82,  there  is  danger 
that  some  of  the  coagulated  casein  may  not  be  com- 
pletely redissolved  and  this,  mixing  with  the  fat, 
makes  the  fat-column  in  the  test-bottle  more  or  less 
pale  and  cloudy,  when  it  should  be  clear  and  usually 
golden  yellow  in  color.  In  addition,  there  is  apt  to 
be  a  collection  of  cloudy  matter  at  the  foot  of  the  fat- 
column,  obscuring  the  line  of  division  and  making 
sharp  reading  difficult.  The  use  of  more  than  17.5  cc. 
of  acid  not  too  weak  may  give  good  results. 

Effect  of  too  strong  acid. — When  the  acid  is  too 
much  above  specific  gravity  1.83,  the  fat-column  is 
dark  in  color.  There  is  a  layer  of  black  material  be- 
low it,  and  the  amount  of  fat  is  difficult  to  read  with 
accuracy.  When  the  acid  is  too  strong,  it  is  possible 
to  secure  accurate  results  by  using  less  than  17.5  cc. 


THE    BABCOCK   TEST  . 


43 


of  acid,  the  exact  quantity  being  determined  by  trying 
different  amounts  of  acid,  until  the  fat-column  obtained 
is  clear  and  yellow.  Strong  acid,  if  allowed  to  stand 
open  to  the  air,  will  in  time  absorb 
enough  moisture  to  reduce  it  to  proper 
strength.  By  far  the  best  plan  is  to 
purchase  the  acid  of  guaranteed  spe- 
cific gravity  1.82  to  1.83,  since  all 
dairy-supply  houses  now  furnish  such 
acid,  and  then  take  pains  to  keep  the 
acid  in  tightly  stoppered  bottles  when 
not  in  use. 

Testing  strength  of  acid. — The 
strength  of  sulphuric  acid  may  be  con- 
veniently tested  by  a  specially  designed 
hydrometer  (Fig  18).  This  instru- 
ment or  acidometer  is  simply  allowed 
to  float  in  the  sulphuric  acid,  which 
must  be  at  60°  F.,  and  the  specific 
gravity  is  read  from  the  scale  where 
it  coincides  with  the  upper  surface  of 
the  liquid,  which  should  be  between 
the  scale-marks  1.82  and  1.83.  No 
acidometer  should  be  used  whose  ac- 
curacy is  not  reliably  guaranteed.  ACID 

Reducing  the  strength  of  strong  acid. — With  the 
aid  of  an  acidometer,  it  is  possible  to  purchase  strong 
sulphuric  acid  and  dilute  it  to  proper  strength.  This 
is  not  advised  for  the  average  worker.  When  this  is 
done,  extreme  caution  must  be  used  in  diluting  the 
acid.  Never  pour  water  into  strong  sulphuric  acid, 
but  always  add  the  acid  to  the  water.  The  amount  of 


FIG.    l8 

HYDROMETER    FOR 

TESTING  STRENGTH 

OF  SULPHURIC 


44  MODERN    METHODS   OF   TESTING   MILK 

dilution  depends  upon  the  strength  of  the  acid  used. 
One  should  start  with  a  small  dilution  and  increase 
gradually  until  the  specific  gravity  of  the  acid  becomes 
1.82  to  1.83.  After  diluting  the  acid  with  water,  the 
mixture  becomes  hot,  and  it  is  necessary  to  allow  it 
to  cool  to  60°  F.  before  testing  with  the  acidometer. 

Useful  indications  regarding  strength  of  acid. — 
After  one  has  acquired  some  skill  in  making  the  Bab- 
cock  test,  one  can  readily  tell  whether  the  acid  is  too 
strong  or  too  weak  from  its  action  when  mixed  with 
milk  in  the  test-bottle.  One  bases  his  judgment  on 
the  rapidity  with  which  the  milk-casein  is  coagulated 
and  redissolved,  and  also  upon  the  quickness  with 
which,  and  the  degree  to  which,  the  mixture  of  acid 
and  milk  turns  dark. 

Keeping  acid  from  air. — The  acid  should  be  kept 
in  tightly  stoppered  bottles,  because,  if  exposed  to  air, 
it  absorbs  moisture  and  becomes  too  weak.  The  stop- 
per should  be  glass,  since  a  common  cork  stopper  is 
soon  destroyed  by  the  acid,  and  even  rubber  is  not 
long  satisfactory. 

Care  in  handling  sulphuric  acid. — Strong  sulphuric 
acid  is  extremely  corrosive  and  is  dangerous  to  han- 
dle except  with  care.  In  contact  with  articles  like 
clothing  or  leather,  it  quickly  ruins  them,  while  on 
the  skin  it  causes  serious  burns  in  a  short  time.  If 
sulphuric  acid  gets  upon  one's  skin,  it  should  be  imme- 
diately and  thoroughly  washed  with  an  abundance  of 
water,  and  this  may  be  followed  by  washing  with  di- 
lute ammonia  or  sodium  carbonate.  In  case  acid  gets 
on  the  clothing,  treat  it  first  with  abundance  of  water 
and  then  with  ammonia.  Red  discoloration  on  cloth- 


THE    BABCOCK    TEST  45 

ing  caused  by  acid  may  be  remedied  by  treatment  with 
ammonia,  if  not  too  long  delayed.  Acid  on  tables, 
floors,  etc.,  may  be  neutralized  by  treatment  with 
washing  soda  or  other  alkali. 

METHODS  OF  TESTING  ACCURACY  OF 
APPARATUS 

The  correctness  of  the  graduation  of  the  glassware 
used  in  the  Babcock  test  is  a  fundamental  condition  of 
accuracy  in  the  results  obtained.  In  some  states  all 
graduated  glassware  used  in  the  Babcock  test  must 
be  tested  by  the  state  and  found  correct  before  its  use 
is  permitted  in  commercial  operations.  Reliable  deal- 
ers guarantee  the  accuracy  of  their  glassware,  and  it 
is  found  to  be  much  more  reliable  than  formerly.  How- 
ever, it  is  a  safe  precaution  always  to  test  new  appa- 
ratus before  using  it.  Testing  graduated  glassware 
is  known  technically  as  calibration. 

Testing  or  calibrating  milk-bottles. — Test-bottles 
which  show  a  variation,  above  or  below,  of  more  than 
one  division,  or  .2  per  cent.,  in  the  10  per  cent,  scale, 
should  not  be  used.  The  different  methods  of  test- 
ing will  now  be  considered. 

(i)  Testing  zvith  special  bottle-tester. — The  quick- 
est method  of  testing  the  accuracy  of  the  scale  of  a 
test-bottle  is  to  use  a  special  device,  which  is  essentially 
a  simple  brass  plunger  (Fig.  19).  This  instrument  is 
divided  into  two  equal  portions,  each  part  being  made 
of  such  a  size  as  to  displace  exactly  one  cubic  centi- 
meter of  liquid.  This  bottle-tester  is  used  as  follows : 
The  test-bottle  is  filled  to  the  zero  mark  with  milk,  or 
one  may  use  water  or,  better,  wood  alcohol,  imparting 


MODERN    METHODS   OF   TESTING    MILK 


color  to  the  water  or  alcohol  by  adding  some  black 
aniline  or  carmine  ink.  Fill  the  bottle  nearly  to  the 
zero  mark  and  then  finish  with  a  pipette  or  dropper, 
adding  a  drop  at  a  time  just 
to  the  mark.  Any  drops  of 
liquid  adhering  to  the  inside 
walls  of  the  neck  must  be  re- 
moved, using  conveniently  a 
strip  of  blotting  or  filter  pa- 
per. The  tester  is  then  slowly 
lowered  into  the  neck  of  the 
test-bottle  until  the  liquid  rises 
half  way  between  the  two 
sections  of  the  instrument, 
when  the  upper  surface  of 
the  liquid  should  be  at  the  5 
per  cent,  mark  (Fig  20),  if 
the  scale  is  correct  to  this 
point.  If  the  surface  of  the 
liquid  is  above  or  below  the 
5  per  cent,  mark,  then  the 
scale  is  incorrect  to  that  ex- 
tent. After  the  accuracy  of 
the  5  per  cent,  mark  is  tested, 
the  instrument  is  then  lowered 
into  the  bottle  until  the  liquid 
rises  about  one-eighth  of  an 

inch    abOVe    the    tOO    of   the    Up- 

£ 

per  section  of  the  tester.  If 
the  upper  surface  of  the  liquid  is  level  with  the  10 
per  cent,  mark,  the  graduation  is  correct  at  that  point. 
The  graduation  of  the  scale  is  regarded  as  correct,  if 


FIG.   20 

TESTING 
MILK-BOTTLE    ACCURACY   OF 
TESTER  MILK-BOTTLE 


THE    BABCOCK   TEST  47 

the  tester  shows  the  5  and  10  per  cent,  marks  to  be 
correct. 

In  explanation  of  the  use  of  this  form  of  bottle-tes- 
ter, it  is  to  be  remembered  that  the  neck  of  the  milk- 
bottle  is  so  graduated  as  to  hold  2  cc.  between  the  o 
and  10  marks;  hence,  the  volume  between  the  o  and 
5  marks  should  be  i  cc.,  and  that  between  the  5  and 
10  marks  should  be  also  I  cc.  The  brass  plunger  is 
so  made  that  each  section  displaces,  or  forces  up  into 
the  neck,  i  cc.  of  liquid,  the  whole  instrument  displac- 
ing 2  cc.  This  tester  therefore  gives  two  tests  of  the 
scale,  one  at  the  5  per  cent,  mark  and  the  other  at 
the  10  mark. 

Some  of  these  instruments  are  made  to  test  the  4 
and  8  per  cent,  points,  so  that  with  two  testers,  one 
can,  if  desired,  test  the  accuracy  of  the  scale  at  the 
4,  5,  8  and  10  points.  There  are  also  testers  of  the 
same  form  made  for  cream-bottles. 

In  using  this  bottle-tester,  the  following  precautions 
are  to  be  observed : 

(1)  Have  the  upper  surface  of  the  liquid  exactly 
on  a  level  with  the  zero  mark  in  the  neck  of  the  test- 
bottle  before  putting  the  tester  in. 

(2)  Clean  the  inside  walls  of  the  neck  of  the  bot- 
tle from  adhering  liquid  before  testing. 

(3)  No  air-bubbles  should  be  allowed  to  adhere  to 
the  tester  when  it  is  below  the  liquid. 

(4)  The  tester  should  be  dry  each  time  before  using. 
(2)    Testing  with   mercury. — From   an   accurately 

graduated  burette  (Fig.  21),  measure  2  cc.  of  clean 
mercury  into  the  bottle  to  be  tested.  Then  push  down 
into  the  neck  of  the  bottle  as  far  as  the  top  line  of 


48 


MODERN    METHODS   OF   TESTING    MILK 


graduation  a  close-fitting  cork  or  plug,  cut  off  square 
at  the  lower  end.  Turn  the  bottle  upside  down,  caus- 
ing the  mercury  to  run  into  the  neck.  The  mercury 
just  fills  the  space  in  the  neck  between  the  o  and  10 
mark,  if  the  graduation  is  accurate.  The  same 
mercury  can  be  used  in  the  same  way  in  test- 
ing one  bottle  after  another  by 
transferring  all  the  mercury 
from  one  bottle  to  another,  which 
may  be  conveniently  done  by 
slipping  a  piece  of  elastic  rub- 
ber tubing  over  the  ends  of  the 
necks  of  the  two  bottles.  In 
using  the  same  mercury  for  test- 
ing one  bottle  after  another,  no 
mercury  must  be  lost  in  trans- 
ferring, and  none  must  be  left 
in  the  bottle  last  tested.  The 
inside  walls  of  the  test-bottle 

must    be    dry    and    dean    m    Qrder 

to  prevent  any  mercury  adhering. 

(3)  Testing  with  water. — The  bottle  to  be  tested 
is  filled  with  water,  slightly  colored  with  carmine  ink, 
or  otherwise,  up  to  the  zero  mark.  The  coloring  of 
the  water  makes  easier  the  reading  of  the  height  of 
the  liquid.  Any  water  adhering  to  the  inside  of  the 
neck  is  removed  by  a  strip  of  blotting  or  filter  paper. 
Then  one  runs  into  the  test-bottle  2  cc.  of  colored  water 
from  a  burette  or  pipette,  graduated  to  twentieths  of 
a  cubic  centimeter.  The  upper  surface  of  the  liquid 
should  be  on  a  level  with  the  10  per  cent,  mark  if  the 
scale  is  correct.  Any  part  of  the  scale  can  be  similarly 


FIG.    21 
BURETTE    AND    SUPPORT 


THE    BABCOCK   TEST  49 

tested,  remembering  that  each  per  cent,  on  the  scale 
should  contain  just  .2  cc.  of  liquid. 

Testing  accuracy  of  pipette. — When  many  pipettes 
are  to  be  tested,  one  runs  into  one  pipette  from  an 
accurately  graduated  burette  (Fig.  21),  17.6  cc.  of 
mercury,  closing  the  lower  end  of  the  pipette.  The 
mercury  should  fill  the  pipette  just  to  the  17.6  cc. 
mark,  if  the  mark  is  correct.  The  same  mercury  can 
be  transferred  to  other  pipettes  in  succession.  Care 
must  be  taken  to  have  the  pipettes  clean  and  dry  in- 
side and  that  all  the  mercury  is  transferred  without 
loss. 

When  only  one  or  a  few  pipettes  need  testing,  wa- 
ter can  be  used,  running  from  a  burette  into  each  pi- 
pette 17.6  cc.  of  water,  which  should  just  fill  the 
pipette  to  the  mark,  if  accurate. 

Testing  accuracy  of  acid  measure. — Ordinarily  the 
acid  measure  does  not  need  testing,  since  a  little  varia- 
tion does  not  affect  the  results.  When  desired,  it  can 
be  tested  by  running  in  water  or  milk  from  a  17.6  cc. 
pipette,  known  to  be  accurate. 

KEEPING  GLASSWARE  CLEAN 

It  is  very  important  that  the  test-bottles  and  the 
pipettes  used  in  the  Babcock  test  should  be  kept  as 
clean  as  possible  from  fat  adhering  to  the  inside  sur- 
face. Unless  a  special  effort  is  made,  the  bottles 
quickly  become  covered  inside  with  a  film  of  fat, 
which  may  be  sufficient  to  increase  appreciably  the 
results  obtained  when  the  bottles  are  used  in  testing. 
The  bottles  should  be  kept  entirely  free  from  any  fat- 


5O  MODERN    METHODS   OF   TESTING    MILK 

film  and  the  wall  should  be  clear  and  bright.     This 
can  be  accomplished  without  serious  trouble. 

As  soon  as  a  test  is  completed  and  the  amount  of 
fat  read,  the  test-bottle,  while  still 
warm,  should  be  emptied.  This 
may  easily  be  done  by  having  a 
large  earthenware  jar  or  crock, 
covered  with  a  board  (Fig.  22), 
in  which  are  several  holes  large 
enough  to  admit  easily  the  necks 
of  test-bottles.  The  bottle  is  in- 
verted, the  neck  run  down  through 
one  of  these  holes,  and  at  the 
same  time  the  bottle  is  shaken  up  and  down  in 
order  to  remove  the  white  calcium  sulphate  de- 
posited on  the  bottom  of  the  bottle  during  the  test. 
Then,  when  one  is  ready  to  clean  up  all  the  bottles 
that  have  been  used,  each  one  is  rinsed  with  8  or  10 


FIG.    22 — WASTE-JAR 
FOR  EMPTYING 
TEST-BOTTLES 


FIG.   23 — TEST-BOTTLE  U1NSEE 


THE    BABCOCK   TEST 


FIG.   24 — TEST-BOTTLE  DRAINING  RACK 

cc.  of  a  solution,  consisting  of  one  ounce  of  potassium 
bichromate   dissolved   in  one  pint  of   sulphuric  acid. 

Then  a  test-bottle  brush 
is  run  once  up  and  down 
the  neck  of  each  bottle, 
and  finally  each  is  well 
rinsed   with   hot   water. 
There     are     available 
several     devices     which 
may  be  found  convenient 
and    time-saving    where 
many    bottles    are    used 
daily.    Among  these  de- 
vices may  be  mentioned 
a  bottle-rinser  (Fig.  23), 
a  drain-rack   (Fig.  24), 
and      a     bottle- 
washer       (Figs. 
2$a,   b,   and   r), 
described     by 
Farrington 
(Bulletin  129, 
Wis.  Agr.  Exp. 
Station,  pp.  22- 

FIG.    25a — BOTTLE-HOLDER,    EMPTY  24)  • 


CHAPTER    IV 


Method  of  Operating  the  Babcock  Test 

In  describing  the  method  of  operating  the  Babcock 
test,  when  determining  the  amount  of  fat  in  milk, 
special  attention  will  be  called  at  each  step  to  such 
difficulties  as  may  occur,  and  emphasis  will  be  placed 
upon  such  precautions  as  experience  has  shown  to  be 
necessary  in  order  to  obtain  accurate  results. 

In  brief  outline,  the  different  steps  may  be  stated 
as  follows : 

i  Mix  thoroughly   sample   of  milk,   which   is  at  60°   to 
7o°F. 

2.  Quickly  fill  pipette  to  mark  with  milk. 

3.  Run  milk  into  test-bottle. 

4.  Fill   acid-measure   to  mark  with  acid  and  pour   into 

test-bottle. 

5.  (i)   Mix  milk  and  acid  thoroughly  by  rotary  motion; 

(2)   let  stand  2  to  5  minutes;  and  (3)   mix  again. 

6.  Put  test-bottles  in  tester   (centrifuge)   and  whirl  4  or 

5  minutes  at  proper  speed. 

7.  (i)  Add  fairly  hot  water  up  to  neck  of  bottles;    (2) 

whirl  one  minute;   (3)  add  hot  water  to  8  or  9  per 
cent,  mark ;  and    (4)    whirl  one  minute. 

8.  Read  results  at  temperature  of  about  130°  F. 

PREPARING   SAMPLES   OF   MILK   FOR   TESTING 

The  milk,  which  should  be  at  a  temperature  of  60° 
to  70°  F.,  is  thoroughly  mixed  by  pouring  from  one 
vessel  to  another  two  or  three  times,  at  least,  imme- 

53 


54  MODERN    METHODS   OF   TESTING    MILK 

diately  before  taking  the  sample  for  testing.  The  spe- 
cial methods  of  preparing  milk  for  sampling  under 
various  conditions  are  fully  considered  in  Chap.  II, 
p.  20.  The  fat  must  be  evenly  distributed  through 
the  milk  just  before  sampling. 

Every  sample  of  milk  should  always  be  tested  in 
duplicate,  that  is,  two  tests  should  be  made  at  the 
same  time.  This  insures  greater  accuracy.  If  the 
results  of  the  duplicate  test  do  not  agree,  there  is  an 
error  somewhere  and  the  work  must  be  repeated.  Also, 
in  case  one  test  is  lost  and  another  sample  can  not  be 
obtained,  the  remaining  test  can  be  used,  and  the  whole 
work  will  not  be  lost. 

TAKING  SAMPLES  OF  MILK  WITH  PIPETTE 

The  measuring  pipette  (Fig.  8,  p.  35),  is  filled  at 
once  after  the  thorough  mixing  of  the  milk.  This  is 
done  by  placing  the  lower  end  of  the  pipette  well  down 
in  the  milk  and  sucking  up  the  milk  until  it  reaches 
a  point  in  the  pipette  somewhat  above  the  mark  around 
its  upper  stem.  Then  the  forefinger,  which  must  be 
dry,  is  quickly  placed  over  the  upper  end  of  the  pi- 
pette before  the  milk  runs  down  below  the  mark.  By 
lightening  the  pressure  of  the  finger  on  the  end  of 
the  pipette,  the  milk  is  allowed  to  flow  out  slowly  un- 
til its  upper  surface  just  reaches  the  mark  on  the 
stem.  Some  practice  is  necessary  before  one  can  eas- 
ily and  rapidly  manipulate  the  pipette  with  accuracy. 

The  pipette  must  be  kept  very  clean.  When  sam- 
ples of  several  different  milks  are  to  be  drawn  in  suc- 
cession, the  pipette  may  be  satisfactorily  rinsed  by 


THE    BABCOCK   TEST 


55 


drawing  it  full  of  the  milk 
next  to  be  sampled,  this  por- 
tion being  thrown  away. 

TRANSFERRING  SAMPLE 

OF   MILK   FROM  PIPETTE 

TO  TEST-BOTTLE 

•  Having  filled  the  pipette 
just  to  the  17.6  cc.  mark,  one 
holds  the  pipette  obliquely  to 
the  bottle,  placing  the  point 
of  its  lower  end  within  the 
neck  and  against  the  side  of 
the  neck  of  the  test-bottle. 
The  right  way  of  holding  the 
pipette  is  .shown  in  Fig.  26. 
By  loosening  the  finger  at 
the  upper  end  of  the  pipette, 
one  allows  the  milk  to  flow 
slowly  down  the  inside  of  the  \N 
neck.  The  small  portion  of 
milk  adhering  to  the  inside  of 
the  pipette  is  nearly  all  carried 
into  the  bottle  by  blowing 
through  the  pipette  several 
times  before  removing  it  from 
the  neck  of  the  bottle.  Not 
a  drop  of  the  milk  should  be  FIG.  26— CORRECT  WAY  OF 
allowed  to  spill  outside  the  HOLDING  PIPETTE  AND 
bottle  in  transferring  from  BOTTLE 

the  pipette. 

It  is  not  intended  to  remove  every  trace  of  milk 
from  the  pipette  into  the  bottle,  since  allowance  for 


MODERN    METHODS   OF    TESTING    MILK 


what  remains  is  made  in  the 
construction  of  the  pipette. 
Special  experiments  having 
shown  that  .1  cc.  of  milk  will 
remain  adhering  to  the  inside, 
the  pipette  is  made  to  hold 
17.6  cc.  to  the  mark,  but  is* 
expected  to  deliver  into  the 
bottle  only  17.5  cc.,  the  exact 
amount  required  for  the  test. 
In  delivering  the  milk,  the 
pipette  must  never  be  held 
perpendicularly  in  a  line  with 
the  neck  of  the  test-bottle, 
running  the  milk  straight 
down  as  shown  in  Fig.  26a, 
since  the  narrow  neck  may 
easily  choke  up  with  milk  and 
run  over  the  top. 

MEASURING  AND  ADDING 

ACID 

When  the  samples  of  milk 
are  in  the  test-bottles,  th^  acid- 
measure   (Fig.   n,  p.  36),  is 
filled  to  the  17.5  cc.  mark  and 
the  acid  (see  p.  42)  is  poured 
FIG.   260 — WRONG  WAY  OF  into  the  test-bottle.     The  acid 
HOLDING  PIPETTE  AND      should  be  at  a  temperature  of 
BOTTLE  60°    to    70°    F.      Much    care 

must  be  exercised  in  pouring 

the  acid  into  the  test-bottle  containing  the  milk.    The 
test-bottle  is  held  in  an  inclined  position,  so  that  the 


THE    BABCOCK   TEST  57 

acid  will  follow  the  inside  wall  down  to  the  bottom, 
and  the  pouring  should  be  slow  and  steady.  Thus 
handled,  the  acid,  being  much  heavier  than  the  milk, 
forms  a  layer  by  itself  at  the  bottom  of  the  bottle, 
while  the  milk  forms  a  separate  layer  by  itself  on  top 
of  the  acid.  While  pouring  in  the  acid,  it  is  well  to 
turn  the  test-bottle  around  slowly  so  the  acid  may  in 
turn  come  in  contact  with  different  portions  of  the 
inside  walls  of  the  neck  and  wash  down  any  adhering 
milk.  Unless  this  is  done,  some  milk  may  remain  on 
the  wall  of  the  neck,  in  which  case  it  will  not  be  prop- 
erly acted  on  by  the  acid,  and  the  fat-column  will  con- 
tain particles  of  undissolved  casein. 

If  one  attempts  to  pour  the  acid  straight  down  the 
neck  of  the  bottle,  two  difficulties  are  liable  to  occur: 
(i)  The  neck  may  easily  choke  up  and  the  acid  over- 
flow on  the  operator's  hands.  (2)  The  acid  may  drop 
into  and  partially  mix  with  the  milk,  in  which  case 
black  particles  may  appear  on  the  upper  surface  of  the 
acid  layer  and  later,  mixing  in  the  fat-column,  may 
interfere  with  accurate  reading  of  the  results. 

Temperature  of  milk  and  acid. — It  is  directed  to 
have  the  milk  and  acid  at  a  temperature  of  60°  to 
70°  F.  before  they  are  placed  in  the  test-bottle.  There 
are  good  reasons  for  this  precaution.  If  the  milk  or 
acid  is  decidedly  cold,  as  may  easily  happen  in  cold 
weather,  the  action  of  the  acid  may  not  be  vigorous 
enough  to  redissolve  completely  the  coagulated  casein, 
thus  producing  white  specks  or  a  cloudy  appearance 
in  and  below  the  fat-column  at  the  end  of  the  test. 
On  the  other  hand,  if  the  milk  or  acid  is  at  too  high 
a  temperature,  as  may  easily  happen  in  hot  weather, 


58  MODERN    METHODS    OF   TESTING    MILK 

the  action  of  the  acid  is  much  the  same  as  if  it  were 
too  strong,  producing  dark-colored  specks  or  a  dark- 
ened appearance  in  and  below  the  fat-column.  Ex- 
perience shows  that  when  the  milk  and  acid  are  at  a 
temperature  between  60°  and  70°  F.,  there  is  no  dan- 
ger of  too  slight  or  too  strong  action  of  acid.  More 
acid  can  be  used  at  lower  temperatures  and  less  at 
higher  temperatures  with  satisfactory  results,  but  this 
involves  experimenting;  the  best  way  will  be  to  use 
the  regular  amount  of  acid  and  regulate  the  tempera- 
ture of  the  milk  and  acid. 

MIXING  MILK  AND  ACID  IN  TEST-BOTTLE 

When  the  measured  amount  of  acid  has  been  placed 
in  the  test-bottle,  the  acid  and  milk  should  be  thor- 
oughly mixed.  This  is  best  done  by  giving  the  bot- 
tle a  rotary  motion,  with  gentle  shaking,  until  the 
whole  mass  becomes  liquid  and  free  from  solid  parti- 
cles of  casein.  Much  motion  up  and  down  should  be 
avoided,  since  milk  might  be  thrown  up  into  the  neck 
of  the  bottle  beyond  reach  of  the  acid,  in  which  case 
coagulated  casein  would  contaminate  the  fat-column 
and  impair  the  results. 

When  the  acid  and  milk  first  mix,  the  casein  is 
coagulated  in  a  somewhat  solid  mass,  which  gradu- 
ally redissolves  as  the  mixing  becomes  complete.  The 
mixing,  once  begun,  should  continue  until  the  casein 
appears  to  be  redissolved.  If  the  operation  of  mixing 
milk  and  acid  is  incomplete  or  is  interrupted,  black 
particles  may  appear  in  the  fat-column  at  the  end  of 
the  test. 

It  is  a  wise  precaution  to  allow  the  bottle  to  stand 


THE    BABCOCK    TEST  59 

2  to  5  minutes  after  the  mixing  appears  complete  and 
then  to  agitate  a  second  time  with  rotary  motion  just 
before  placing  in  the  tester. 

The  action  of  the  sulphuric  acid  upon  the  water  and 
organic  solids  of  the  milk  produces  a  marked  degree 
of  heat,  as  soon  as  the  acid  and  milk  begin  to  mix. 
The  color  of  the  solution  becomes  yellow  at  first  and 
then  passes  through  varying  darker  shades  of  yellow 
to  violet,  brown  and  finally  dark-brown,  if  the  acid  is 
of  the  right  strength.  (See  p.  42.)  The  coloration  is  due 
to  the  action  of  the  acid  upon  the  milk-sugar  and  milk- 
casein.  Too  strong  acid  produces  a  dense  black  color. 
In  samples  of  milk  containing  too  much  bichromate  of 
potash,  the  color  becomes  greenish  black. 

Samples  of  milk  that  have  been  preserved  for  some 
time  with  bichromate  or  formalin,  especially  when  the 
preservative  is  used  in  larger  than  usual  amounts,  re- 
quire more  time  and  agitation  to  redissolve  the  coag- 
ulated casein  than  do  ordinary  samples,  since  these 
preservatives  harden  the  coagulated  casein.  (  See  p.  29) . 

WHIRLING  THE  TEST-BOTTLES 

The  test-bottles  containing  the  mixture  of  milk  and 
acid,  after  being  agitated  a  second  time  as  stated  above, 
are  placed  in  the  centrifugal  tester  (p.  37),  and 
whirled.  This  is  better  done  soon  after  the  milk  and 
acid  are  mixed,  but  it  may  be  delayed  without  harm 
for  24  hours,  in  which  case,  however,  the  bottles 
should  be  placed  in  water  at  160°  to  180°  F.  for  15 
or  20  minutes  before  whirling. 

An  even  number  of  bottles  should  be  whirled  at  the 
same  time  and  they  should  be  placed  about  the  disc 


6O  MODERN    METHODS   OF   TESTING   MILK 

in  pairs  opposite  to. each  other,  so  that  the  equilibrium 
of  the  tester  will  not  be  disturbed.  When  all  the  sam- 
ples to  be  tested  are  placed  in  the  tester,  the  cover 
is  placed  on  the  jacket  and  the  machine  turned  for  4 
or  5  minutes  at  proper  speed,  600  to  1,200  revolutions 
per  minute,  according  to  the  diameter  of  the  centri- 
fugal disc.  (p.  40.) 

The  whirling  brings  the  fat  to  the  top  of  the  mix- 
ture in  the  test-bottle.  The  whirling  of  the  bottles 
should  never  be  done  without  having  the  cover  on  the 
jacket,  for  two  reasons:  (i)  The  cover  prevents  the 
cooling  of  the  fat  in  the  test-bottles  during  whirling, 
and  (2)  the  operator  is  protected  from  injury  in  case 
a  bottle  should  break  and  scatter  its  contents  while 
being  whirled. 

In  the  case  of  hand-testers,  it  may  be  necessary  to 
put  hot  water  in  the  jacket  in  cold  weather  in  order 
to  keep  the  bottles  warm  enough. 

ADDING   HOT   WATER   TO   THE   TEST-BOTTLES 

When  the  bottles  have  been  whirled  4  or  5  minutes, 
moderately  hot  water  is  added  to  each  bottle  until  the 
contents  come  to  the  lower  end  of  the  neck.  The 
water  may  be  added  with  a  pipette  or  by  means  of 
any  convenient  arrangement.  The  cover  of  the  ma- 
chine is  replaced  and  the  bottles  are  whirled  at  full 
speed  for  one  minute.  Hot  water  is  again  added  to 
the  bottles  until  the  fat,  which  is  lighter  than  the  rest 
of  the  liquid,  rises  in  the  neck  to  the  8  or  9  per  cent, 
mark.  One  must  be  careful  never  to  run  the  water 
above  the  10  per  cent.  mark.  The  whirling  is  then  re- 
peated for  one  minute  at  full  speed. 


THE    BABCOCK    TEST  6l 

Three  points  deserve  attention  in  this  connection: 
(i)  The  temperature  of  the  water  added,  (2)  the 
kind  of  water  used  and  (3)  the  number  of  times  water 
is  added. 

(1)  The  temperature  of  the  water  added  should  be 
above  120°  F.    The  aim  in  general  should  be  to  have 
the  temperature  of  the  fat  at  the  close  of  whirling  at 
130°  or   140°   F.,  and  the  temperature  of  the  water 
added  should  have  reference  to  this  fact.     However, 
any  effect  of  too  hot  or  too  cold  water  can  be  remedied 
after  the  final  whirling  by  adjusting  the  temperature 
as  needed. 

(2)  Clean,  pure,  distilled  water  is  the  best  form  to 
use  and,  next,  soft  rain  water.     Hard  water  may  seri- 
ously affect  the   results.     Objections   to   hard   water 
may  in  most  cases  be  overcome  by  thorough  boiling 
or  by  previous  treatment  with  a  few  drops  of  sul- 
phuric acid. 

(3)  Some  operators  add  Jthe  hot  water  only  once, 
filling  the  bottle  to  near  the  top  of  the  neck  immedi- 
ately after  the  first  whirling.     The  advantage  of  ad- 
ding the  water  in  two  portions  is  that  the  fat  is  washed 
free  from  adhering  impurities,  since  the  fat-column  is 
often  mixed  with  various  particles  which  render  the 
reading  uncertain  and  frequently  too  high. 

READING  RESULTS  IN  PERCENTAGE  OF  FAT 

After  the  last  whirling  is  completed,  the  test-bottles 
are  removed  from  the  tester,  one  at  a  time,  in  order 
to  read  the  results  of  the  test.  To  ascertain  the 
amount  of  fat,  hold  the  test-bottle  upright,  having  the 
graduated  scale  of  the  neck  of  the  bottle  on  a  level 


62  MODERN    METHODS   OF   TESTING    MILK 

with  the  eye.  Notice  the  divisions  marking  the  high- 
est and  lowest  limits  of  the  fat-column.  The  differ- 
ence between  them  gives  directly  the  per  cent,  of  fat 
in  the  milk  tested.  The  readings  can  be  made  accu- 
rately to  one-half  of  a  division,  that  is,  to  one-tenth  of 
one  per  cent.  Some  test-bottles  are  provided  with  a 
regulator  which  moves  the  bottom  of  the  fat-column 
to  a  level  with  the  nearest  numbered  mark. 

In  connection  with  the  measuring  of  the  fat-column, 
the  following  points  deserve  attention :  ( i )  Using  divi- 
ders to  assist  in  reading,  (2)  the  temperature  of  the 
fat-column,  (3)  the  upper  and  lower  limits  of  the 
fat-column,  (4)  the  correct  appearance  of  the  fat- 
column,  (5)  defects  in  appearance  of  the  fat-column. 

(1)  If  one  uses  test-bottles  not  provided  with  a  reg- 
ulator for  adjusting  the  level  of  the  fat-column,  the 
reading  of  the  percentage  of  fat  on  the  scale  may  be 
made   with   less   liability   of  error  by   measuring  the 
length  of  the  fat-column  with  a  pair  of  dividers,  one 
point  of  which  is  placed  at  the  bottom  and  the  other 
at  the  upper  limit  of  the  fat-column.     The  dividers 
are  then  removed  and  one  point  is  placed  on  the  zero 
mark  of  the  scale  on  the  bottle  used,  when  the  other 
point  will  be  at  the  exact  per  cent,  of  fat  in  the  milk 
tested. 

(2)  The  temperature  of  the  fat,  when  it  is  read  or 
measured,   should  be  above   120°    F.  and  not  above 
140°  F.,  preferably  about  130°  F.     This  will  insure 
sharply  defined  upper  and  lower  limits  of  the  fat-col- 
umn.    In  case  the  contents  of  the  bottles  are  below 
120°  F.,  the  bottles  should  be  placed  for  15  or  20  min- 
utes in  water  that  has  a  temperature  of  130°  to  140°  F., 


THE    BABCOCK   TEST 


before  the  reading  is  made.  This  usually  needs  to  be 
done  in  cold  weather,  when  hand-testers  are  used, 
especially  if  no  hot  water  has  been  placed  in  the  jacket 
during  the  whirling.  If  the  fat  is  above  150°  F.,  it 
should  be  allowed  to  cool  to  140°  F.  or  below  before 
reading  the  results.  Too  high  temperatures  give  too 
high  results,  because  the  fat-column  expands. 

(3)  The  line  of  division  between  the  fat-column  and 
the  liquid  beneath  is  nearly  a  straight  line  when  the 
testing  is  properly  done,  and  one  need  have  no  doubt 
about  the  reading  of  the  scale  at  this  point.     But  the 
upper    surface    of   the    fat-column    is 
concave    instead    of    straight,    which 
may  cause  some  uncertainty  as  to  the 
exact    point    at    which    the    reading 
should  be   made   on   the   scale.     The 
correct   reading   is   taken   at   the   line 
where  the  upper  surface  of  the  fat- 
column  meets  the  sides  of  the  neck, 
the  very  highest  point  at  which  the 
fat-column     is     seen.       The     reading 
should   not  be   made   from   the   dark 
line  or  meniscus  lower  down,  which 
is    caused    by    the    refraction   of   the 
curved  surface.     The  points  at  which 
the  readings  should  be  made  are  shown 
in    Fig.    27,    indicated   as   A   and    B. 
Results  read  this  way  agree  with  those 
obtained  by  gravimetric  analysis.   The 
objection  may  be  raised  that  we  get  too  high  results 
by  reading  from  the  extreme  top  points  of  the  fat- 
column,  just  as  if  the  upper  surface  were  straight  at 


- 

—    3 

A 

—  —  2 

i 

F 

[G.   27 

MEASURING 

FAT-COLUMN 

64  MODERN    METHODS    OF   TESTING    MILK 

these  points  instead  of  concave.  While  there  is  such 
an  apparent  error,  the  excessive  reading  thus  caused 
is  only  enough  to  make  up  for  the  loss  of  fat  which 
can  not  be  separated  from  the  rest  of  the  liquid  by 
centrifugal  force  and  brought  into  the  fat-column.  The 
amount  of  fat  thus  left  in  the  mixture  of  milk-serum 
and  acid  is  ordinarily  about  .2  per  cent,  and  this  is 
about  the  amount  of  excess  obtained  by  the  approved 
method  of  reading  the  upper  limit  of  the  fat-column. 

(4)  The  fat  appearing  in  the  neck  of  the  test-bot- 
tle at  the  end  of  a  successful  test  is  of  a  clear,  yellow 
color,  and  the  line  of  division  between  its  lower  limit 
and  the  acid  solution  beneath  it  is  sharply  distinct. 
However,  the  fat  is  apt  to  be  light-colored  in  the  case 
of  milk  from  cows  far  along  in  lactation. 

(5)  The  fat-column  may  show  certain  defects,  if 
the  conditions  of  the  test  have  not  been  properly  car- 
ried out,  among  which  are  (a)  black  particles  below 
or  above  or  in  the  fat-column,  or  a  darkened  appear- 
ance of  the  whole  column  of  fat;  (b)  white  particles 
below  or  above  or  in  the  fat-column,  or  a  cloudy  ap- 
pearance of  the  whole  column;  and   (c)   bubbles  on 
the  surface. 

(a)  Black  particles  in  the  neck  of  the  test-bottle  at 
the  end  of  the  test,  or  a  darkened  appearance  of  the 
fat  itself,  are  due  to  one  or  more  of  the  following 
causes:  (i)  Too  strong  acid  (above  1.83  specific  grav- 
ity), (2)  too  much  acid  (more  than  18  cc.),  (3)  too 
high  temperature  of  the  milk  or  acid  (over  75°  F.), 
(4)  allowing  milk  and  acid  to  stand  in  test-bottle  too 
long  before  mixing,  (5)  allowing  the  acid  to  drop 


THE    BABCOCK   TEST  65 

through  the  milk  when  poured  into  the  test-bottle, 
(6)  interrupting  the  mixing  of  the  milk  and  acid  af- 
ter beginning  and  before  completion. 

(b)  White  particles  of  undissolved  casein  below  or 
above  or  in  the  fat-column,  or  a  cloudy  appearance  of 
the  fat,  are  due  to  one  or  more  of  the  following  causes : 
(i)  Too  weak  acid  (below  1.82  specific  gravity),  (2) 
insufficient  amount  of  acid  (less  than  17  cc.),  (3)  too 
low  temperature  of  milk  or  acid  (below  60°  F.),  (4) 
incomplete  mixing  of  milk  and  acid,   (5)   insufficient 
speed  of  tester. 

Sometimes  when  the  fat  is  not  clear,  good  results 
may  be  obtained  by  allowing  the  bottles  to  cool  enough 
for  the  fat  to  harden  some,  and  then  warming  in  wa- 
ter at  140°  F.  before  reading. 

(c)  Bubbles  of  gas,  appearing  as  foam  on  the  top 
of  the  fat-column,  are  generally  due  to  the  use  in  the 
test-bottle  of  hard  water  containing  carbonates.     This 
condition  may  be  prevented  by  adding  to  the  water, 
previous  to  use,  a  few  drops  of  sulphuric  acid.    When 
the  foam  appears  and  interferes  with  the  reading,  a 
few  drops  of  alcohol  are  put  on  the  top  of  the  fat-col- 
umn and  the  reading  is  at  once  made.     The  alcohol 
causes  the  bubbles  to  disappear  and  produces  a  sharp 
line  of  division  between  the  fat  and  alcohol.     If  the 
alcohol  is  allowed  to  be  in  contact  with  the  fat  for 
some  time  before  the  reading  is  made,  the  alcohol  and 
fat  mix  and  increase  the  height  of  the  fat-column,  thus 
producing  misleading  results. 


66  MODERN    METHODS   OF   TESTING    MILK 

OUTLINE  STATEMENT  OF  SOME  SPECIAL 
PRECAUTIONS 

1.  Always  make  tests  in  duplicate. 

2.  Make  sure  that  the  sample  is  a  representative  one. 

3.  Have  the  temperature  of  the  milk  and  acid  at 
60°  to  70°  F.  before  putting  in  test-bottle. 

4.  Use  only  acid  of  right  strength. 

5.  Mix  milk  and  acid  thoroughly  as  soon  as  acid 
is  added. 

6.  Mix  a  second  time  after  a  short  interval. 

7.  Make  sure  that  the  tester  runs   at  right  speed 
and  does  not  jar. 

8.  Use  only  clean,  soft  water  in  filling  bottles. 

9.  Read  bottles  before  they  cool  and  at  about  130°  F. 

10.  To  insure  accuracy,  read  each  test  twice. 

SOME  MODIFICATIONS  OF  THE  BABCOCK  TEST 

One  frequently  sees  references  in  dairy  literature 
to  other  forms  of  tests  for  milk.  As  a  matter  of  in- 
formation, we  will  notice  a  few  of  the  modifications  of 
the  Babcock  test  together  with  other  forms  that  are 
in  use,  giving  good  results. 

The  Russian  Test. — This  is  a  modification  of  the 
Babcock  test,  differing  mainly  in  respect  to  some  of 
the  mechanical  details.  A  special  automatic  pipette  is 
used  (Fig.  28),  a  special  form  of  test-bottle  (Fig.  280), 
the  neck  being  separate  from  the  rest  of  the  bottle,  and 
also  a  special  form  of  acid-measure.  The  pipette  and 
acid-measure  are  one-half  the  usual  size.  The  milk  and 
acid  are  run  into  the  bottle  very  easily,  and  the  bot- 
tles are  filled  with  hot  water  automatically  while  the 
machine  is  in  motion,  the  tester  also  being  of  a  special 
form. 


THE     BABCOCK     TEST 


67 


The  Gerber  Butyrometer. — Special  forms  of  tes- 
ter, test-bottle,  etc.,  are  used.  The  test  uses  n  cc.  of 
milk,  10  cc.  of  sulphuric  acid  (1.825  specific  gravity), 


i-s 


FIG.  28 

AUTOMATIC  "RUSSIAN"  PIPETTE 


FIG.  280 
'RUSSIAN"  TEST-BOTTLE 


and  i  cc.  of  amyl  alcohol.     The  operations  are  carried 
out  about  the  same  as  in  the  Babcock  test. 

The  "Sinacid"  (no  acid)  Test. — The  distinctive  fea- 
ture of  this  test  is  that,  in  place  of  sulphuric  acid,  it 
uses  a  patented  mixture,  consisting-  of  sodium  phosphate 
and  citrate,  which,  unlike  sulphuric  acid,  is  entirely  free 
from  any  dangerous  properties;  it  uses  also  a  colored 


68  MODERN    METHODS   OF   TESTING    MILK 

alcoholic  solution.  After  mixing  the  "sinacid"  liquid 
with  the  milk,  the  mixture  is  heated  to  200°  F.  for  5 
minutes  before  being  whirled  in  the  tester.  The  re- 
sults do  not  always  appear  to  agree  closely  with  those 
given  by  other  tests,  according  to  the  reports  of  some 
operators.  There  is,  moreover,  some  natural  preju- 
dice against  using  a  process,  any  part  of  which  is 
patented. 

Gerber's  "Sal"  Test.— Gerber  has  just  published  a 
method  in  which  no  acid  is  used.  The  full  details  are 
not  given,  since  the  method  is  to  be  patented.  Good 
results  are  reported. 


CHAPTER   V 


Method  of  Testing  Cream  by  the  Babcock  Test 

The  Babcock  test  can  be  used  in  ascertaining  the 
amount  of  fat  in  cream,  but  certain  precautions  and 
modifications  are  necessary  to  insure  correct  results. 
A  special  form  of  test-bottle  is  generally  used.  Spe- 
cial pains  must  be  taken  in  sampling  cream.  For 
strictly  accurate  work,  the  cream  sample  must  be 
weighed  for  testing. 

USE  OF  MILK  TEST-BOTTLES  IN  TESTING 
CREAM 

Test-bottles  used  in  testing  milk  can  be  used  in 
testing  cream  only  under  special  conditions.  Cream 
containing  over  10  per  cent,  of  fat  will  fill  the  neck 
of  the  test-bottle  too  full  for  measurement,  when  we 
take  1 8  grams  (about  17.5  cc.)  to  test.  This  difficulty 
may  be  overcome  in  two  ways :  ( i )  By  using  a  sample 
of  cream  less  than  18  grams,  and  (2)  by  dividing  an 
1 8-gram  sample  in  roughly  equal  parts  between  two  or 
more  bottles,  according  to  its  richness  in  fat.  In  the 
former  case  the  per  cent,  of  fat  read  is  increased  by 
a  correction  to  be  considered  later.  In  the  second  case, 
the  tests  are  made  as  in  case  of  milk  and  the  per- 
centages found  in  the  different  bottles  are  added,  the 
sum  being  the  per  cent,  of  fat  in  the  cream  tested.  The 
volume  of  cream  in  each  test-bottle  is  always  made  up 

69 


MODERN    METHODS    OF   TESTING    MILK 


to  about  17.5  cc.  by  adding  water  to 
the  cream  and  mixing  before  adding 
acid. 

SPECIAL  CREAM-TESTING 
BOTTLES 

To  test  in  one  bottle  an  1 8-gram 
sample  of  cream  containing  over  10 
per  cent,  of  fat,  the  neck  must  be 
made  to  hold  more  than  the  neck  of 
a  milk-bottle,  that  is,  more  than  2  cc. 
This  additional  space  must  be  ob- 
tained ( i )  by  using  a  neck  of  larger 
diameter,  keeping  the  length  the  same 
as  in  the  milk-bottle  or  (2)  by  mak- 
ing the  neck  longer,  keeping  the  diam- 
eter the  same.  There  is  this  objection 
to  making  the  necks  of  test-bottles  too 
large  in  diameter,  that  the  divisions 
on  the  scale  come  nearer  together 
and  the  reading  of  the  results  is  less 
accurate.  If  the  neck  is  made  long 
enough  to  allow  as  fine  graduation 
as  in  the  milk-testing  bottles,  then 
the  bottles  are  too  long  to  use  in  an 
ordinary  tester. 

Bulb-necked  cream-bottle. — Both 
of  the  difficulties  mentioned  above  are 
overcome  by  having  a  bulb  made  in 
the  neck  of  the  bottle  (Fig.  29).  In 
this  cream-testing  bottle  the  gradua- 
tion is  as  fine  as  in  the  milk-testing 
bottles,  the  smallest  division  repre- 
senting .2  per  cent.,  and  the  scale  ex- 


s 
Ls 

fc 


/\ 


FIG.   29 
BULB-NECKED 
CREAM -BOTTLE 


TESTING   CREAM    BY   THE   BABCOCK    TEST 


tends  from  o  to  25  per  cent.  Hence,  in  these  bottles 
we  can  use  18  grains  of  cream,  provided  the  cream 
does  not  contain  over  25  per  cent,  of  fat,  while,  with 
cream  testing  over  25  and  up  to  50  per  cent.,  a  9- 
gram  sample  can  be  used  for  the  test.  In  using  this 
form  of  bottle,  care  must  be  observed 
when  water  is  added  near  the  close 
of  the  test.  Neither  the  lower  nor  the 
upper  surface  of  the  fat-column  must 
be  allowed  to  come  in  the  bulb,  since, 
obviously,  it  is  impossible  then  to  read 
the  results.  This  style  of  bottle  is  also 
made  with  a  scale  measuring  50  per 
cent.,  the  smallest  divisions  being  .25 
per  cent. 

Straight-necked  cream-bottles.  — 
The  other  varieties  of  cream-testing 
bottles  are  straight-necked,  varying  in 
respect  to  (i)  diameter,  (2)  length 
of  neck,  and  (3)  fineness  of  gradua- 
tion. These  vary  in  length  from  the 
ordinary  size  to  9  and  10  inches,  the 
longer  sizes  requiring  special  testers. 
In  capacity,  the  necks  vary  from  6  to 
20  cc.,  which  is  equivalent  to  30  to  100  per  cent.,  when 
an  i8-gram  sample  of  cream  is  used.  In  fineness  of 
graduation,  the  smallest  divisions  vary  in  different  bot- 
tles from  .2  to  i  per  cent.  One  type  of  straight-necked 
bottle  is  shown  in  Fig.  30.  For  strictly  accurate  work, 
bottles  graduated  to  .2  per  cent,  should  be  used ;  and 
the  use  of  bottles  whose  finest  division  is  more  than 
.5  per  cent,  should  be  condemned,  except  for  rough 
work. 


FIG.  30 

STRAIGHT-NECKED 
CREAM -BOTTLE 


72  MODERN    METHODS   OF   TESTING    MILK 

CREAM-TESTING  SCALES 

For  weighing  samples  of 
cream,  a  set  of  accurate 
scales  is  required.  Differ- 
ent forms  are  illustrated  in 
Figs.  31  and  32.  Scales 
with  agate  bearings  are 
much  preferable  to  other 
.forms,  since  the  agate  bear- 
ings do  not  rust.  Torsion  balances  and  those  with 
steel  bearings  are  liable  to  rust  when  kept  in  damp 


FIG.   31 
CREAM-TESTING  SCALES 


FIG.    32 — CREAM-TESTING    SCALES 


places,  and  this  in  time  makes  them  unreliable  for 
accurate  work.  The  scales  should  be  kept  in  perfect 
condition  and  tested  for  accuracy  from  time  to  time. 

METHOD  OF  SAMPLING  CREAM 

Cream,  from  which  the  test  sample  is  to  be  taken, 
whether  for  part  of  a  composite  sample  or  for  direct 
testing,  must  be  made  as  uniform  as  possible  through- 
out its  mass.  The  best  method  of  sampling  any  but 


TESTING   CREAM    BY   THE   BABCOCK   TEST  73 

small  amounts  of  cream  is  by  means  of  a  sampling- 
tube  (Fig.  5,  p.  27),  which  must  be  cleaned  for  each 
sample  before  using.  Frozen  cream  must  be  thawed 
and  mixed  before  sampling.  Large  lots  of  dried 
cream  or  partially  churned  cream  can  not  be  sam- 
pled with  complete  accuracy.  Cream  adhering  to 
the  outside  of  the  sampler  should  not  be  allowed  to 
go  into  the  test  sample. 

METHOD  OF  KEEPING  CREAM  SAMPLES 

In  keeping  composite  samples  of  cream,  the  same 
precautions  are  to  be  observed  as  in  the  case  of  milk 
(p.  30).  With  thick  cream  special  effort  may  be 
needed  to  cause  the  preservative,  especially  potassium 
bichromate,  to  dissolve  and  be  distributed  through 
the  sample.  This  may  be  done  by  warming  the  jars 
and  mixing  the  cream  carefully  by  a  gentle  rotary  mo- 
tion. 

PREPARATION  OF  SAMPLES  FOR  TEST 

Before  taking  from  the  cream  sample  the  amount 
to  be  used  in  the  test,  the  cream  must  have  its .  fat 
evenly  distributed.'  To  accomplish  this,  the  cream  is 
heated  to  105°  or  110°  F.  until  it  is  quite  fluid.  As 
recommended  by  Hills  (Bulletin  100,  Vermont  Exp. 
Sta.,  p.  5),  the  cream  is  passed  through  a  small  sieve 
(Fig.  33),  such  as  is  commonly  used  in  kitchens.  Any 
remaining  lumps  found  in  the  sieve  are  rubbed  through 
the  meshes  by  the  finger,  after  which,  the  cream  is 
thoroughly  mixed  by  pouring  from  one  cup  to  another. 
The  sample  is  then  quickly  taken  for  testing. 


74  MODERN    METHODS   OF   TESTING    MILK 

WHY  USE  OF  PIPETTE  IS  INACCURATE  FOR 
CREAM 

The  use  of  a  pipette  in  measuring  cream  samples 
is  inaccurate  for  the  following  reasons :  ( i )  More  fat 
adheres  to  the  inside  of  a  pipette  than  in  case  of 
milk,  the  error  increasing  with  the  thickness  of  cream. 
(2)  The  weight  of  cream  decreases  as  the  per  cent, 
of  fat  in  cream  increases,  since  milk-fat  is  lighter 

than  the  other 
constituents 
of  cream.  The 
scale   of  the   test-bottle   is 
based    on    the    use    of    18 
grams  of  material,  but  the 
amount  of  cream  that  oc- 
33  cupies  the  volume  filled  by 

CREAM-SAMPLING    SIEVE  jg  gfams  Qf  milk  (  ^   ^ 

is  found  to  be  more  or  less  below  18  grams  according 
to  the  increased  percentage  of  fat  in  the  cream,  run- 
ning even  below  17  grams  in  very  rich  cream.  (3) 
Separator  cream  is  more  or  less  filled  with  bubbles  of 
air,  and  ripened  cream  contains  gases  produced  by 
fermentation.  These  decrease  the  weight  of  a  given 
volume  of  cream. 

For  the  preceding  reasons,  the  result  of  trying  to 
measure  by  pipette  a  sample  of  cream  to  be  used  for 
testing  its  fat  content  is  that  less  cream  will  be  used 
than  should  be,  and  therefore  the  results  will  be  too 
low.  Any  system  of  volumetric  measurement  pro- 
posed is  open  to  some  uncertainty  and  inaccuracy. 
The  use  of  a  pipette  in  testing  cream  is  justifiable  only 
for  work  that  is  not  expected  to  be  strictly  accurate. 


TESTING  CREAM   BY  THE  BABCOCK   TEST  75 

If  one  uses  a  pipette  in  measuring  cream  for  test- 
ing, somewhat  more  accurate  results  are  generally  ob- 
tained by  measuring  18  cc.  of  cream  and  also  rinsing 
the  pipette  into  the  test-bottle  with  a  small  amount  of 
water.  Pipettes  are  obtainable  which  have  an  18  cc. 
mark  as  well  as  a  17.6  cc. 

WEIGHING  SAMPLE  OF  CREAM 
The  operation  of  weighing  cream  is  simple.  One 
places  the  empty  test-bottle  on  one  pan  of  the  scales 
and  balances  it  by  a  slide-weight  or  some  form  of 
counterpoise.  One  then  places  an  1 8-gram  weight 
on  the  other  pan,  after  which  the  pipette  is  rilled  with 
cream  somewhat  above  the  17.6  cc.  mark,  and  this  is 
run  into  the  bottle,  the  last  portion  being  run  in  more 
slowly,  until  the  two  scale-pans  just  counterbalance 
each  other.  A  little  practice  enables  one  to  weigh 
the  exact  amount  rapidly.  In  case  the  amount  of 
cream  taken  in  the  pipette  is  not  enough,  agitate 
the  sample,  draw  a  little  more  into  the  pipette  and 
run  this  slowly  into  the  bottle  until  it  counter-bal- 
ances the  weight.  In  case  too  much  cream  is  run 
into  the  bottle,  the  surplus  can  easily  be  withdrawn 
by  the  pipette.  No  cream  must  be  allowed  to  get  on 
the  outside  of  the  bottle  or  on  the  scale-pan  while  the 
weighing  is  done. 

Using  less  than  18  grams. — In  case  of  very  rich 
cream  it  is  preferable  to  use  9  grams  for  a  sample,  in 
which  case  the  reading  of  the  fat-column  is  multiplied 
by  2 ;  or  the  1 8-gram  sample  may  be  divided  between 
two  cream-bottles,  in  which  case  water  should  be  ad- 
ded to  each  bottle  so  as  to  bring  the  liquid  to  about 
1 8  cc.  in  volume.  The  results  of  the  test  in  the  two 


76  MODERN    METHODS   OF   TESTING   MILK 

bottles  are  added.  It  is  more  convenient  after  a  little 
practice  to  weigh  exactly  9  or  18  grams  than  to  run 
in  an  approximate  amount  of  cream  and  weigh  that 
accurately. 

In  case  one  uses  any  amount  less  than  18  grams  for 
a  sample,  it  is  necessary  to  correct  as  follows  the  per 
cent,  of  fat  read:  Divide  18  by  the  number  of  grams 
of  cream  used  and  multiply  the  result  by  the  per  cent, 
of  fat  read  in  the  test.  For  example,  one  uses  13.5 
grams  of  cream  and  the  result  reads  15.6  per  cent,  of 
fat.  Divide  18  by  13.5,  which  gives  1.33,  and  multiply 
this  by  15.6,  which  equals  20.8  per  cent.,  the  true  per- 
centage of  fat  in  the  sample. 

SPECIAL  POINTS  ABOUT  TESTING  CREAM 

When  one  uses  18  grams  of  cream  in  one  test-bot- 
tle, the  operation  is  completed  as  in  testing  milk. 
When  one  uses  less  than  18  grams  in  one  test-bottle, 
enough  water  is  added  to  make  the  volume  about  18 
cc.  Thus,  when  an  1 8-gram  sample  is  divided  be- 
tween two  bottles,  or  a  9-gram  sample  in  one  bottle 
is  used,  we  add  9  cc.  of  water  to  the  cream,  mix  them 
thoroughly  and  then  proceed  as  usual.  The  water  and 
cream  should  always  be  well  mixed  before  adding 
acid. 

When  it  is  difficult  to  get  a  clear  column  of  fat,  it 
may  be  remedied  by  the  use  of  a  little  less  acid,  the 
exact  amount  to  be  found  by  trial.  In  general,  the 
richer  the  cream,  the  less  acid  is  required,  15  cc.  often 
being  enough.  The  full  amount  of  acid  is  used  when- 
ever the  cream  is  diluted  with  water  before  adding 
acid,  as  in  the  case  of  taking  a  9-gram  sample,  or  di- 
viding an  1 8-gram  sample  between  two  cream-bottles. 


TESTING   CREAM    BY   THE   BABCOCK   TEST  77 

Sometimes  it  is  well  to  let  the  bottles  stand  a  little 
while  after  being  mixed  with  the  acid,  until  the  mix- 
ture turns  dark,  before  whirling. 

When  the  liquid  just  below  the  fat-column  is  milky 
and  the  fat  looks  cloudy  and  light,  exact  reading  is 
difficult.  In  such  cases  the  bottles  may  be  placed  in 
water  at  130°  to  140°  F.  for  15  or  20  minutes  before 
whirling,  or,  if  this  fails,  the  fat  may  be  solidified  by 
placing  the  bottles  in  cold  water  after  the  last  whirl- 
ing and  then  heated  to  130°  or  140°  F.  before  reading. 

READING  THE  PER  CENT.   OF  FAT  IN   CREAM- 
TESTING  BOTTLES 

In  reading  the  results  of  a  cream  test,  more  care 
is  needed  than  in  testing  milk,  especially  if  wide- 
necked  bottles  are  used  in  which  the  finest  divisions 
represent  .5  per  cent,  or  more.  For  accurate  work, 
one  should  use  narrow-necked  cream-bottles  in  which 
the  results  can  be  read  to  .2  per  cent. 

In  no  case,  should  there  be  used  in  the  same  cream- 
ery at  the  same  time  different  varieties  of  cream-bot- 
tles, having  necks  of  widely-varying  diameter.  It 
has  been  shown  by  Webster  ( Bulletin  No.  58,  Bureau 
of  Animal  Industry,  Dairy  Division,  U.  S.  Dept.  of 
Agr.),  that  the  results  obtained  with  cream-bottles 
having  necks  of  varying  diameters  are  wide  apart, 
when  read  in  the  ordinary  manner.  This  is  due  to 
the  fact  that  the  depth  of  the  meniscus  increases  with 
the  diameter  of  the  neck  of  the  bottle.  The  wider  the 
neck  the  greater  the  error,  this  being  in  the  direction 
of  too  high  results. 


78  MODERN    METHODS    OF   TESTING    MILK 

SAMPLING    AND    TESTING    GATHERED    CREAM 

In  many  dairying  communities,  hand  separators  are 
used  by  dairymen,  and  cream  instead  of  milk  is  sent 
to  the  creamery.  The  cream  of  several  patrons  is 
gathered  at  intervals  by  some  one  employed  for  the 
purpose.  The  ideal  plan  would  be  to  keep  each  pa- 
tron's cream  separate  until  delivered  and  sampled  at 
the  creamery,  but  usually  the  different  lots  of  cream, 
being  comparatively  small  in  amount,  are  not  kept 
separate,  being  put  together  indiscriminately  into  large 
cans  on  the  gathering  wagons,  as  a  matter  of  conven- 
ience. Under  such  circumstances,  it  becomes  neces- 
sary to  obtain  at  each  farm  a  sample  of  the  patron's 
cream  before  it  is  mixed  with  other  lots.  Outlining 
the  general  procedure,  the  person  collecting  cream  car- 
ries a  sample  bottle  for  each  patron,  puts  into  this  a 
sample  of  cream,  takes  this  to  the  creamery  and  either 
tests  at  once  or  makes  up  a  composite  sample  for  each 
patron  from  the  samples  gathered  during  a  period  of 
one  or  two  weeks.  These  composite  samples  are  care- 
fully prepared  and  kept  in  the  manner  described  on 
pp.  24-31  and  p.  73.  The  test  for  fat  is  made  accord- 
ing to  the  directions  given  on  pp.  69-77. 

Taking  up  the  details,  the  method  of  sampling  gath- 
ered cream  on  farms  is  carried  out  in  the  following 
manner:  The  person  who  collects  the  cream  is 
equipped  with  (i)  large  cans  into  which  different  lots 
of  cream  are  poured  after  weighing  and  sampling,  (2) 
spring  balance,  (3)  two  pails  for  weighing  cream  and 
mixing  before  sampling;,  (4)  sampling-tube,  and  (5) 
a,  case  containing  sample-bottles.  At  each  dairy  the 


TESTING    CREAM    BY    THE    BABCOCK    TEST  79 

collector  takes  the  weighing  and  sampling  equipment 
from  the  wagon,  including  one  sample-bottle  marked 
so  as  to  identify  the  individual  patron  whose  cream  is 
put  into  it.  The  cream  is  poured  from  one  pail  to 
another  twice  or  more  until  it  is  completely  mixed,  and 
then  it  is  quickly  weighed,  after  which  a  sample  is  at 
once  taken  and  placed  in  the  sample-bottle.  The  sam- 
ples should  be  taken  by  means  of  a  sampling-tube  (p. 
27),  which,  after  using,  should  be  rinsed  each  time 
with  the  cream  next  to  be  sampled.  This  is  done  simply 
by  lowering  the  tube  in  the  usual  manner  to  the  bottom 
of  the  pail  that  holds  the  cream  and  then  drawing  the 
tube  out  and  allowing  all  the  cream  to  run  back  into 
the  pail.  After  this  rinsing,  the  sample  is  drawn  and, 
after  allowing  the  cream  adhering  to  the  outside  of  the 
tube  to  drain  off  for  a  few  seconds,  the  contents  of  the 
tube  are  transferred  to  the  sample-bottle.  In  case  a 
patron  has  more  than  one  pailful  of  cream,  a  sample  is 
taken  from  each  weighing,  the  same  weighing-pail 
being  used  each  time ;  in  this  case  the  different  samples 
are  put  into  one  sample-bottle. 

After  each  patron's  cream  is  weighed  and  sampled, 
it  is  poured  into  the  collector's  large  can.  The  sam- 
ple-bottles are  carried  to  the  creamery  and  the  con- 
tents of  each  transferred  to  the  corresponding  com- 
posite-sample jar.  The  collecting  bottles  must  be 
thoroughly  cleaned  and  dried  before  using  again.  If 
any  difficulty  is  experienced  in  the  management  of  the 
composite  samples,  it  is  advisable  to  test  each  sam- 
ple of  cream  after  it  reaches  the  creamery  and  not  pre- 
pare composite  samples. 

Cream  that  is  frozen  or  sour  can  not  be  handled  sat- 


86  MODERN    METHODS   OF   TESTING    MILK 

isfactorily  for  sampling  or  testing  and  should  not  be 
taken.  For  judging  and  scoring  the  quality  of  cream 
according  to  the  method  given  in  Chapter  XIV,  one 
may  make  use  of  the  collected  sample  before  it  is 
put  into  the  composite  sample. 


CHAPTER    VI 

Method  of  Testing  Skim-Milk,  Whey,   Butter, 
Cheese,  Etc. 

Dairy  products,  such  as  cheese,  condensed  milk,  and 
milk  powders  can  be  tested  for  fat  by  the  Babcock 
test,  and  also  by-products  such  as  skim-milk,  butter- 
milk and  whey.  In  general,  the  operation  is  carried 
out  as  in  testing  milk,  but  some  special  modifications 
are  necessary. 

METHOD    OF  TESTING   SKIM-MILK,  WHEY,   ETC. 

In  testing  materials  containing  only  .2  or  .3  per  cent, 
of  fat,  two  difficulties  are  experienced :  ( I )  In  the 
ordinary  test-bottle,  the  reading  of  so  small  amounts 
of  fat  can  not  be  easily  done  with  accuracy.  (2)  Some 
fat  is  necessarily  left  in  the  mixture  of  acid  and  milk- 
serum,  which  may  constitute  an  important  factor  when 
the  total  fat  content  is  small. 

Special  forms  of  test-bottles  used  in  testing  whey, 
etc. — To  enable  one  to  make  readings  of  small  amounts 
of  fat  with  increased  accuracy,  special  forms  of  double- 
necked  test-bottles  have  been  devised,  which  are  so 
graduated  as  to  enable  readings  to  be  made  as  low 
as  .01  per  cent.  (Figs.  34  and  35.)  In  using  these 
bottles,  the  milk  and  acid  are  delivered  into  the  larger 
neck,  the  fat  being  driven  up  into  the  small  neck  by 
the  hot  water  added  toward  the  end  of  the  test. 

8 1 


82 


MODERN    METHODS   OF    TESTING    MILK 


Enough  water  is  added  to  bring  the  fat-column  into 
the  middle  of  the  small  neck.  In  mixing  milk  and 
acid  and  in  running  in  hot  water,  care  must  be  taken 
to  prevent  any  liquid  but  fat  going  into  the  small  neck 
or  fine  measuring-tube.  The  stoppers  in  the  bottles 


FIG.  34  FIG.  35 

BOTTLES  FOR  TESTING  SKIM-MILK 

are  used  to  adjust  the  fat-column  for  reading.  These 
double-necked  bottles  should  be  placed  in  the  tester 
in  such  a  way  that  the  filling-tube  is  toward  the  center, 
thus  avoiding  the  danger  of  having  any  fat  caught 
between  this  tube  and  the  side  of  the  bottle  when  re- 
suming the  upright  position  after  whirling. 

Separating  fat  from  mixture  in  bottle. — Attention 
has  previously  (p.  64)  been  called  to  the  difficulty  ex- 
perienced in  separating  all  the  fat  from  the  mixture 


TESTING   SKIM-MILK,    WHEY,    CHEESE,    ETC.  83 

of  acid  and  milk-serum.  Under  ordinary  conditions 
of  working",  materials  low  in  fat,  like  skim-milk,  may 
fail  to  give  up  to  the  fat-column  .05  or  even  .1  per 
cent,  of  fat.  Some  double  the  reading  of  fat  when  it 
is  below  .1  per  cent,  in  order  to  make  allowance  for 
the  unseparated  fat.  The  fat  may  be  separated  from 
the  rest  of  the  liquid  more  completely  by  proceeding 
as  follows :  Use  20  cc.  of  sulphuric  acid,  whirl  the  bot- 
tles at  full  speed  one  or  two  minutes  longer  than 
usual  and  read  the  fat  when  at  a  temperature  of  130° 
to  140°  F.  Steam-turbine  testers,  which  keep  the  bot- 
tles hot,  give  best  results.  Any  test  of  these  by-pro- 
ducts showing  less  than  .05  per  cent,  of  fat  is  open  to 
the  suspicion  of  being  defective. 

Skim-milk  and  buttermilk  are  treated  alike.  In 
working  with  whey,  it  is  noticeable  that  after  adding 
acid  the  mixture  turns  dark  very  slowly,  due  to  the 
presence  of  less  sugar  and  to  the  absence  of  casein. 
Less  than  the  usual  amount  of  acid  is  sufficient  for 
whey,  8  or  10  cc.  frequently  being  sufficient. 


METHOD  OF  TESTING  CHEESE 

In  applying  the  Babcock  test  to  cheese,  it  is  neces- 
sary to  prepare  the  sample  in  a  special  way  and  to 
weigh  the  amount  used.  A  9-gram  sample  is  a  con- 
venient amount  to  use,  in  which  case  the  reading  of 
fat  is  multiplied  by  2;  or  an  1 8-gram  sample  may  be 
divided  between  two  cream-bottles,  the  final  readings 
being  added.  Cream-testing  bottles  graduated  to  .2 
per  cent,  divisions  should  be  used. 


84  MODERN    METHODS    OF    TESTING    MILK  * 

Sampling  cheese  for  fat-test.— Since  different  por- 
tions of  the  same  cheese  vary  in  composition,  special 
means  must  be  used  to  get  a  representative  sample. 
The  sample  for  testing  is  prepared  as  follows :  When 
a  cheese  can  be  cut,  a  narrow,  wedge-shaped  seg- 
ment is  taken,  reaching  from  the  outer  edge  to  the 
center.  This  is  cut  into  strips  and  passed  through  a 
meat-grinding  machine  two  or  three  times.  This  mass 
is  carefully  mixed,  and  from  this  a  9-gram  sample  is 
weighed  into  a  cream-testing  bottle,  or  a  4.5-gram 
sample  into  an  ordinary  milk-testing  bottle. 

When  cheese  can  not  be  cut,  samples  are  obtained 
by  a  cheese-trier.  If  possible,  three  plugs  should  be 
drawn,  one  at  the  center,  one  about  an  inch  from  the 
outer  edge,  and  one  at  a  point  half  way  between  the 
other  two.  If  only  one  plug  can  be  drawn,  this  should 
be  taken  at  a  point  about  half  way  between  the  mar- 
gin and  center.  The  plugs  should  be  taken  perpen- 
dicular to  the  end  surface  of  the  cheese  and  should 
reach  either  entirely  through  the  cheese  or  just  half 
way.  The  plugs  should  be  made  fine  by  grinding  or 
cutting  and  carefully  mixed  before  weighing  samples. 
In  preparing  samples,  they  should  not  be  exposed  to 
the  air  longer  than  necessary,  since  loss  of  moisture 
should  be  prevented  as  much  as  possible  before  w^eigh- 
ing. 

Testing  sample  of  cheese. — The  sample  is  weighed 
into  the  bottle.  Then  one  adds  about  15  cc.  of  hot 
water  in  the  test-bottle  and  agitates  until  the  water 
disintegrates  the  cheese ;  this  may  be  hastened  by  add- 
ing a  few  cubic  centimeters  of  acid,  and  keeping  the 
bottle  in  slightly  warm  water.  When  no  more  lumps 


TESTING    SKIM-MILK,    WHEY,    CHEESE,    ETC.  £5 

are  seen  in  the  liquid,  17.5  cc.  of  sulphuric  acid  is 
added.  The  test  is  then  completed  in  the  usual  way. 
To  obtain  the  per  cent,  of  fat  in  the  cheese,  if  less 
than  1 8  grams  is  used,  multiply  the  reading  of  fat 
by  1 8  and  divide  by  the  number  of  grams  of  cheese 
used  in  the  test. 

METHOD    OF   TESTING    BUTTER 

The  Babcock  test  has  not  been  adapted  to  deter- 
mine accurately  the  amount  of  fat  in  butter.  A  mass 
of  butter  is  so  variable  in  its  composition,  owing  to 
the  uneven  distribution  of  water,  that  it  is  difficult  to 
obtain  a  representative  sample  when  only  a  small 
amount  is  used.  Since  butter  contains  over  80  per 
cent,  of  fat,  a  sample  of  less  than  9  grams  must  be 
used  in  a  test-bottle  made  to  measure  less  than  40 
per  cent,  of  fat.  .  Approximate  results  can  be  obtained 
by  observing  certain  precautions. 

Preparing  sample  of  butter. — With  a  butter-trier 
draw  several  samples,  aggregating  4  to  8  ounces. 
Place  these  samples  in  a  fruit- jar  or  composite-sam- 
ple bottle,  melt  completely  by  placing  in  fairly  hot 
water  with  the  jar  closed;  then  remove  from  hot  wa- 
ter and  shake  vigorously  for  one  or  two  minutes,  after 
which  moderate  agitation  is  continued  until  the  but- 
ter solidifies.  The  cooling  may  be  hastened  by  hold- 
ing the  jar  under  a  stream  of  cold  water,  continuing 
to  shake  the  bottle  vigorously  until  the  butter  hardens. 

Testing  sample  of  butter. — On  a  cream-scale  place 
a  bottle  of  the  form  shown.  After  balancing  the  bot- 
tle, one  takes  on  the  point  of  a  knife  from  different 


86 


MODERN    METHODS    OF    TESTING    MILK 


parts  of  the  sample  of  buUer,  prepared  as  above  de- 
scribed, small  pieces  of  butter  and  places  them  in  the 
funnel-shaped  tube  of  the  bottle  until  the  sample  weighs 
9  grams.  The  bottle  is  then  placed  in  hot 
water  until  the  butter  melts  and  runs  into 
the  test-bottle.  The  fat  adhering  to  the 
inside  wall  of  the  funnel  is  washed  down 
into  the  bottle  with  8.8  cc.  of  hot  water 
and  the  same  amount  of  sulphuric  acid 
(8.8  cc.)  is  added.  After  the  contents 
are  thoroughly  mixed,  the  bottle  is  placed 
in  a  tester  and  whirled  for  about  5  min- 
utes. To  read  the  result,  fill  the  funnel- 
shaped  tube  with  hot  water,  which  raises 
the  fat-column  in  the  graduated  neck. 
By  gently  pressing  down  or  gently  draw- 
ing up  the  rubber  cork  at  the  top  of  the 
graduated  neck,  the  fat-column  may  be 
moved  in  the  graduated  neck  so  as  to 
bring  the  lower  end  of  the  fat-column 
level  with  zero  mark,  which  is  indicated 
by  a  ring  below  the  bulb.  The  percent- 
age of  fat  is  read  directly.  Before  read- 
ing the  test,  let  the  bottle  stand  for  ten 
minutes  in  water  at  120° — I3O°F. 


FIG.    30 

BOTTLE  FOR  USE 

IN    TESTING 

BUTTER 


GRAY'S    RAPID    TEST    FOR   WATER    IN    BUTTER 

The  method  described  below  for  the  determination 
of  water  in  butter  has  been  recently  devised  by  Mr. 
C.  E.  Gray,  Assistant  Dairyman  in  the  Dairy  Division, 
Bureau  of  Animal  Industry,  U.  S.  Department  of  Ag- 
riculture. (Circular  No.  100,  Dec.  31,  1906.)  The 


TESTING    SKIM-MILK,    WHEY,    CHEESE,    ETC.          87 

operation  requires  15  to  20  minutes.  The  principle  of 
the  test  depends  on  the  separation  of  water  from  but- 
ter by  distillation  in  the  presence  of  a  slightly  volatile 
•mixture  of  high  boiling  point  which  does  not  -mix 
with  water.  The  apparatus  will  be  furnished  by 
dairy-supply  houses. 

Apparatus. — The   following   apparatus   is   required 
for  the  test: 

1 i )  Balance    and    weights. — A    cream-testing   bal- 
ance   (see  p.  72),  sensitive  to  0.025  gram;  and  two 
weights,  one  5-gram  and  one  lo-gram. 

(2)  Graduate. — Measuring  6  cc. 

(3)  Burner. — A  gas  burner  or  an  alcohol  lamp. 

(4)  Paper. — Parchment,  perfectly  dry,  5  by  5  inches 
in  size. 

(5)  Special  testing  apparatus. — This  includes  three 
essential   pieces,    (a)    a   flask    (A   Fig.   36a)    holding 
about  70  cc.,  (b)  a  receiving  bulb  with  graduated  tube 
(C  Fig.  36a),  and   (c)   a  condensing  jacket   (E  Fig. 
36a).    The  receiving  bulb  is  connected  with  flask  A  by 
means  of  a  rubber  stopper  (B).     G  is  a  ground  glass 
stopper  fitting  tightly  into  the  tube  above  the  gradu- 
ated scale.     Each  stopper  and  tube  should  be  marked 
so  that  each  stopper  shall  always  be  used  with  its  cor- 
responding tube.     The  graduation  of  the  tube  is  done 
after  the  glass  stopper  is  fitted,  so  that  the  zero  mark 
is  the  end  of  the  stopper.    Each  mark  of  the  graduated 
scale  represents  0.2  per  cent,  of  water  when  a  lo-gram 
sample  of  butter  is  used.    The  glass  condensing  jacket 
(E  Fig.  36a)  is  connected  to  the  graduated  tube  by  a 
rubber  stopper  (D  Fig.  36a). 


83 


MODERN    METHODS    OF   TESTING    MILK 


i" 


J\se 


6 

RAY'S  APPARATUS 

r.HADY  F03USE  IN     Sample. 


(6)  Rubber  stoppers.  —  The  rubber 
stopper  B  is  so  acted  upon  in  testing 
by  the  heat  and  reagent,  that  a  new 
one  is  required  after  about  100  tests. 

Reagents.  —  Reagents  are  required 
as  follows: 

(1)  Amyl  reagent.  —  This  consists  of 
a  mixture  of  5  parts  of  amyl  acetate 
and   i   part  of  amyl  valerianate,  and 
these  must  be  entirely  free  from  water- 
soluble  impurities. 

(2)  Alcohol.  —  This  is  used  for  burn- 
ing when  gas  is  not  available. 

Operation  of  the  test.  —  The  details 
of  the  method  of  determining  water 
in  butter  are  performed  as  follows  : 

(1)  Preparation     of     sample  —  See 
p.  85. 

(2)  Weighing   sample.  —  Place    on 
each  pan  one  sheet  of  parchment  paper 
and   balance   accurately.      Weigh   ex- 
actly 10  grams  of  sample  (see  p.  75), 
plucing  in  center  of  paper. 

(3)  Transferring  sample  to  flask.  — 
The    paper,    containing   the    lo-gram 
sample,  is  folded  in  such  a  shape  that 
the  paper  and  butter  may  be  slipped 
mto  ^as^  ^  without  losing  any  of  the 


AddinS 


reagent.—  Fill  the 


TESTING   SKIM-MILK,    WHEY,    CHEESE,    ETC.          89 

graduate,  which  must  be  dry,  with  amyl  reagent  to  the 
6  cc.  mark  and  pour  into  flask  A. 

(5)  Connecting  the  apparatus. — Connect  the  appa- 
ratus as  shown  in  Fig.  36a,  fill  the  condensing  jacket 
E  with  cool  water  to  within  one  inch  of  the  top   (F 
Fig.  36a)  and  remove  the  glass  stopper. 

(6)  Distilling  the  water  from  the  butter. — Heat  the 
bottom  of  flask  A  over  the  flame  of  the  burner.     The 
butter  soon  melts,  mixes  with  the  amyl  reagent,  and 
later  the  water  passes  as  steam  into  the  receiving  bulb 
(C),  in  which  it  is  condensed  and  held.     The  conden- 
sation in  the  graduated  part 'of  the  tube  must  be  care- 
fully watched  and  the  steam  not  allowed  to  go  higher 
that  the  15  per  cent,  mark,  in  order  to  avoid  risk  of 
losing  water.     If  it  goes  higher 'than  this,  remove  the 
flame   for  a  short  time.     If  the  mixture  in  flask  A 
shows  a  tendency  to  foam  over,  remove  the  flame.     In 
case  of  continued  foaming,  cool  the  flask  and  contents, 
add  about  2  cc.  more  of  amyl  reagent  and  continue 
heating. 

(7)  How  to  know  when  the  distillation  is  complete. 
—When  the  mixture  in  the  flask  becomes  brown  and 

all  crackling  noise  in  boiling  ceases,  the  water  has  all 
been  driven  from  the  flask.  This  usually  requires  from 
5  to  8  minutes. 

(8)  Disconnecting  apparatus. — After  completing  the 
distillation,  flask  A  is  disconnected  from  stopper  B  and 
the  glass  stopper  G  is  firmly  placed  in  tube  C.     The 
tube  is  then  inverted,  transferring  the  water  from  the 
receiving   tube   into   the   graduated   tube,   care   being 
taken  not  to  allow  any  water  to  be  lost  through  the 


QO  MODERN    METHODS    OF    TESTING    MILK 

small  bent  tube  inside  the  bulb.  The  water  is  then 
poured  from  the  condensing  jacket,  after  which  the 
jacket  may  be  removed. 

(9)  Separating   amyl   reagent   from   water. — Some 
amyl  reagent  is  distilled  with  the  water,  but  does  no 
harm  as  they  can  be  easily  separated.    This  is  done  as 
follows:     Hold  the  receiving  bulb  in  the  palm  of  the 
hand  and  the  stoppered  end  away  from  the  body ;  then 
raise  to  a  horizontal  position  and  swing  at  arm's  length 
sharply  downward  to  the  side.    This  is  repeated  several 
times  until  the  line  of  separation  between  the  water 
and  amyl  reagent  is  sharply  distinct,  no  amyl  reagent 
being  seen  with  the  water,  or  vice  versa.     The  tube 
should  then  be  held  a  short  time  with  the  stoppered 
end  downward  and  the  amyl  reagent  in  the  bulb  agi- 
tated in  order  to  rinse  down  any  water  adhering  to 
the  sides  of  the  bulb. 

(10)  Reading  the  test. — After  cooling  the  tube  and 
contents,  the  percentage  of  water  may  be  read  directly 
from  the  scale,  when  a  lo-gram  sample  is  used.     The 
water  is  in  the  bottom  of  the  tube.     The  reading  is 
made  to  the  lower  part  of  the  meniscus. 

Cleaning  the  apparatus. — The  flask  and  tube  should 
always  be  perfectly  dry  before  being  used.  An  occa- 
sional cleaning  with  washing  soda  in  hot  water  or 
other  cleansirig  mixture  will  keep  the  apparatus  suffi- 
ciently clean.  After  making  the  test,  tube  C  is  emptied 
by  holding  the  stoppered  end  downward,  removing  the 
stopper  and  allowing  contents  to  flow  out  quickly.  The 
tube  is  further  cleaned  and  dried  by  swinging  in  the 
manner  described  above  under  (9). 


TESTING    SKIM-MILK,    WHEY,    CHEESE,    ETC. 


Improved  form  of  Gray's 
apparatus. — The  Wagner  Glass 
Works,  of  New  York,  has  de- 
vised an  improved  form  of  ap- 
paratus for  Gray's  test  (Fig. 
36b.  It  is  simple,  durable  and 
conveniently  operated.  The  wa- 
ter content  of  the  butter  is  col- 
lected in  the  graduated  bore  as 
rapidly  as  distilled  from  the 
butter,  and  the  result  may  be 
read  directly  from  the  grad- 
uated bore  without  swinging  or 
otherwise  changing  the  position 
of  the  apparatus.  There  are  no 
stoppers  to  remove,  to  replace, 
or  to  lose.  Steps  (8)  and  (9) 
(pp.  89-90)  are  obviated  by 
this  improved  apparatus. 

FIG.  36b 

METHODS    OF    TESTING       WAGNER^S  IMPROVED  FORM 
CONDENSED    MILK  OF  GRAY-S  WATER.TEST 

For  condensed  milk  containing  no  added  sugar. — 

(1)  Weigh  9  grams  into  a  milk-testing  bottle,  add 
about  10  cc.  of  water,  then  the  usual  amount  of  acid. 
Complete  test  as  for  milk.    Multiply  fat-reading  by  2. 

(2)  Weigh  40  grams  of  the  well-mixed  sample  into 
a  100  cc.  glass  cylinder,  such  as  is  used  in  the  alkaline- 
tablet  test  (Fig.  38,  p.  104).  Add  water  to  the  100  cc. 
mark  and  shake  until  well  mixed.     Then,  with  a  17.6 
cc.  pipette,  take  for  testing  a  sample  of  this  solution, 
representing  7   grams   of   the   undiluted   sample,   and 


Q2  MODERN    METHODS    OF   TESTING    MILK 

complete  the  test  as  usual.  Multiply  the  fat-reading 
by  18  and  divide  by  7  to  find  the  correct  per  cent,  of 
fat  in  the  sample. 

(3)  Approximate  results  may  be  obtained  by  di- 
luting a  measured  amount  of  condensed  milk  with  an 
equal  volume  of  water,  agitating  the  mixture  until 
uniform.  Then  take  sample  for  testing  with  a  17.6 
cc.  pipette  and  proceed  as  usual.  The  per  cent,  of  fat 
read  is  multiplied  by  2. 

For  condensed  milk  containing  added  sugar. — 
Many  brands  of  condensed  milk  contain  added  cane 
sugar,  which  in  testing  is  so  blackened  by  the  acid  as 
to  make  the  results  unreliable.  This  trouble  can  be  over- 
come by  special  treatment  devised  by  Farrington. 
Make  a  solution  of  40  grams  of  condensed  milk  in 
100  cc.  of  water,  as  directed  above  in  (2).  With  a 
17.6  cc.  pipette,  measure  the  same  amount  as  for  a 
milk  test  into  a  milk-testing  bottle.  Add  about  3  cc. 
of  the  sulphuric  acid  used  in  the  test  and  mix  the 
acid  and  milk  by  shaking  vigorously.  The  acid  is  added 
to  coagulate  the  curd  and  enclose  the  fat,  allowing 
the  sugar  to  separate  in  the  surrounding  liquid.  The 
curd  is  compacted  into  a  lump  by  whirling  the  test- 
bottles  in  a  steam-turbine  tester  at  high  speed  and  at 
a  temperature  of  200°  F.  After  this  whirling,  the 
bottles  are  taken  from  the  tester  and  the  liquid  portion, 
containing  much  of  the  sugar,  is  carefully  poured 
from  the  neck  without  breaking  the  lump  of  curd. 
Then  an  addition  of  10  cc.  of  water  is  made  to  the 
test-bottles,  the  curd  is  shaken  up  to  wash  out  more 
sugar,  and  again  3  cc.  of  sulphuric  acid  added.  The 
bottles  are  again  whirled  and  the  liquid  portion  de- 


TESTING  SKIM-MILK,  WHEY,  CHEESE,  ETC.  93 

canted.  Then  the  test  is  completed  by  adding  10  cc. 
of  water,  17.5  cc.  of  sulphuric  acid,  and  proceeding  as 
usual.  Correct  the  fat-reading  by  multiplying  by  18 
and  dividing  by  7. 

METHOD  OF  TESTING  FOR  FAT  IN  INFANT 
FOODS 

Some  infant  foods  contain  so  much  sugar  that,  like 
sweetened  condensed  milk,  it  is  impossible  to  use  the 
Babcock  test  unmodified.  Cochran  recommends  a 
method  for  the  determination  of  fat  in  such  cases, 
which  he  has  found  very  useful  (Journal  of  the  Amer- 
ican Chemical  Society,  Vol.  27,  p.  908).  A  double- 
tubed  test-bottle  is  used,  the  larger  tube  reaching  only 
a  short  distance  into  the  bowl  of  the  bottle. 

To  determine  fat  in  sweetened  condensed  milk,  make 
a  solution  of  the  condensed  milk  in  the  manner  given 
above  under  (2).  Of  this  solution  put  17.5  cc.  in  the 
test-bottle,  add  9  cc.  of  80  per  cent,  acetic  acid  and 
9  cc.  of  strong  sulphuric  acid.  Mix  the  acids  and  milk 
and  set  the  bottle  in  hot  water  until  the  mixture  in 
the  bottle  turns  a  coffee-brown  color.  Then  remove 
the  bottle,  cool,  add  15  cc.  of  ether  and  mix  thoroughly 
with  the  liquid.  The  flask  is  again  placed  in  hot  wa- 
ter and  the  ether  allowed  to  evaporate.  A  layer  of 
fat  will  appear  floating  on  the  surface  of  the  liquid. 
By  pouring  hot  water  into  the  side  tube,  the  liquid 
fat  is  raised  into  the  graduated  tube,  where  its  amount 
can  be  read.  The  reading  is  corrected  by  multiplying 
by  18  and  dividing  by  7. 

In  the  case  of  powdered  infant  foods,  like  malted 
milk,  weigh  6  grams  of  the  powder  into  the  bottle, 


94  MODERN    METHODS   OF   TESTING    MILK 

add  17.5  cc.  of  water,  dissolve  the  powder  as  com- 
pletely as  possible,  and  proceed  as  above.  Multiply 
the  reading  by  3. 

METHOD   OF  TESTING   DRIED   MILK    OR  MILK 
POWDER 

Successful  means  of  drying  milk  have  recently  been 
devised,  and  products  are  appearing  on  the  market  in 
the  form  of  dried  skim-milk  and  dried  milk.  These 
materials  are  in  the  form  of  fine  flaky  or  powdery 
substances.  Owing  to  the  great  advantages  of  hand- 
ling milk  in  such  forms,  these  products  are  destined 
to  find  extensive  use,  and  the  desirability  of  testing 
them  is  obvious. 

The  Babcock  test,  when  applied  to  these  materials, 
gives  results  much  below  the  truth.  The  writer  has 
obtained  quite  satisfactory  results  by  a  combination  of 
the  Gottlieb  and  Babcock  methods  of  determining  fat. 
The  process  used  is  as  follows :  Dissolve  10  grams  of 
milk  powder  in  100  cc.  of  water.  Take  10  cc.  of  this 
solution  in  a  100  cc.  glass  cylinder  (Fig.  38,  p.  104). 
Add  i  cc.  of  strong  ammonia  and  shake  until  thor- 
oughly mixed  with  the  solution.  Then  add  the  fol- 
lowing reagents,  one  after  the  other,  shaking  vigorously 
after  each  addition  before  adding  the  next  material: 
10  cc.  of  92  per  cent,  alcohol,  25  cc.  of  washed  ether, 
and  25  cc.  of  gasoline  or,  better,  petroleum  ether 
(boiling  point  below  80°  C.).  The  cylinder  is  closed 
with  a  tightly-fitting,  moistened  cork  stopper.  The 
contents  of  the  cylinder,  after  thorough  shaking,  are 
poured  into  a  200  cc.  beaker,  the  cylinder  being  rinsed 
with  a  little  gasoline,  and  this  being  added  to  the 


TESTING  SKIM-MILK,  WHEY,  CHEESE,  ETC.  95 

beaker.  The  beaker  is  then  placed  on  a  steam-bath 
or  in  boiling  water  and  kept  there  until  the  ether,  alco- 
hol and  gasoline  are  completely  evaporated.  The  re- 
maining liquid  is  then  poured  into  a  milk-testing  bot- 
tle, the  beaker  is  rinsed  with  a  little  ether,  which  is 
also  added  to  the  test-bottle.  The  test-bottle  is  then 
placed  in  boiling  water  a  few  minutes  to  evaporate 
the  ether.  After  cooling  the  contents  of  the  test-bot- 
tle to  about  70°  F.,  one  adds  17.5  cc.  of  sulphuric  acid 
and  completes  the  operation  as  in  the  case  of  milk  by 
the  Babcock  test.  The  reading  is  multiplied  by  18. 
In  some  cases,  as  in  dried  skim:milk,  it  will  be  desira- 
ble to  make  the  original  solution  more  concentrated 
by  having  20  or  more  grams  in  100  cc.  of  solution. 
The  following  precautions  must  be  observed  in  using 
this  method: 

(1)  The  milk-powder  solution  must  be  made  uni- 
form before  sampling. 

(2)  The  shaking  of  the  mixture  must  be  vigorous 
and  thorough  after  the  addition  of  each  of  the  reagents 
used. 

(3)  The  evaporation  of  the  reagents  added  must  be 
complete;   otherwise,   the  final   results   are  apt  to  be 
too  high. 

(4)  The  evaporation  must  not  be  carried  so  far  as 
to  cause  any  appearance  of  solid  particles  in  the  liquid. 
When  this  happens,  the  fat-column  contains  dark  ma- 
terial, which  makes  the  results  uncertain. 

This  method  is  applicable  to  skim-milk,  whey  and 
buttermilk,  which  do  not  usually  give  high  enough  re- 
sults by  the  Babcock  method. 


CHAPTER   VII 


Methods  of  Testing  the  Acidity  of  Milk  and  Milk 
Products 

It  is  often  necessary  to  know  how  much  acid  is 
present  in  milk,  cream,  whey,  etc.  The  amount  of 
acid  in  milk  may  be  a  suggestive  indication  of  the 
age  of  milk  and  of  its  care.  In  butter-making,  the 
uniformity  of  the  product  depends  largely  upon  the 
ripening  of  cream,  which  can  be  well  controlled  only 
by  knowing  its  acidity.  In  cheese-making,  it  is  at 
times  important  to  know  whether  milk  contains  too 
much  acid  and  it  is  also  quite  essential  to  have  some 
knowledge  of  the  amount  of  acid  present  in  the  milk 
and  whey  at  different  stages  of  the  operation. 

THE    CAUSES    OF   ACIDITY    IN    MILK    AND    ITS 
PRODUCTS 

We  may  distinguish  two  kinds  of  acidity  in  milk 
and  its  products:  (i)  Apparent  acidity,  and  (c)  acid- 
ity due  to  lactic  acid.  The  apparent  acidity  is  due  to 
the  presence  in  normal  milk  of  casein  and  acid  phos- 
phates, which  have  the  power,  like  free  acids,  of  neu- 
tralizing alkalis.  This  apparent  acidity  in  fresh  milk 
is  about  .07  or  .08  per  cent,  on  the  average.  It  varies 
with  different  conditions,  increasing,  for  instance,  with 
advance  of  lactation. 

Acidity  due  to  lactic  acid  is  formed  in  milk  after  it 
is  drawn,  and  is  caused  by  the  action  of  certain  forms 

96 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS      97 

of  bacteria  upon  milk-sugar.  In  general,  when  milk 
contains  over  .10  per  cent,  of  acid,  it  may  safely  fye 
assumed  that  it  contains  some  lactic  acid.  The  amount 
of  lactic  acid  present  in  milk  may  be  approximately 
found  by  subtracting  .10  from  the  total  amount  of 
acid  apparently  present.  However,  in  speaking  of  the 
acidity  of  milk,  we  usually  mean  the  total  acidity,  and 
not  that  due  to  lactic  acid  alone.  One  can  not  com- 
monly detect  a  sour  taste  in  milk  that  has  a  total  acidity 
under  .3  per  cent. 

GENERAL  PRINCIPLES  OF  TESTING  ACIDITY 

The  method  of  determining  the  amount  of  acid  in 
milk  and  its  products  is  based  upon  the  well-known 
chemical  action  taking  place  between  acids  and  alka- 
lis. Whenever  we  bring  together  in  solution  an  acid 
and  an  alkali,  they  combine  with  each  other  and  form 
a  third  compound,  the  acid  and  alkali  disappearing  as 
such.  The  acid  and  alkali  are  said  to  neutralise  each 
other  and  the  process  is  called  neutralization.  For 
example,  if  we  add  together  some  hydrochloric  (muri- 
atic) acid  and  sodium  hydroxide  (caustic  soda)  in 
right  proportions,  we  shall  have  neither  hydrochloric 
acid  nor  caustic  soda,  but  a  new  compound,  sodium 
chloride  (common  salt),  which  has  been  formed  by 
the  action  of  the  acid  and  alkali  upon  each  other.  The 
hydrochloric  acid  used  in  the  experiment  tastes  sour 
and  biting,  while  the  caustic  soda  solution  has  a  pecu- 
liar odor,  feels  soapy  on  the  skin,  and,  if  strong  enough, 
destroys  the  skin.  After  these  two  compounds  are 
brought  together  in  proper  proportions,  there  is  no 


98  MODERN    METHODS   OF   TESTING    MILK 

longer  observed  any  sour  taste  of  acid  or  soapy  feel- 
ing or  odor  of  alkali,  because  the  acid  and  alkali  have 
neutralized  each  other  and  have  combined  to  form 
simply  common  salt,  the  presence  of  which  is  noticed 
by  its  taste.  The  solution  is  said  to  be  neither  alkaline 
nor  acid,  but  neutral. 

USE  OF  INDICATORS  IN  TESTING  ACIDITY 

In  working  with  acids  and  alkalis,  it  is  necessary 
to  have  some  simple  means  of  knowing  when  a  solu- 
tion is  acid,  alkaline  or  neutral  (neither  acid  nor  alka- 
line). This  can  be  found  by  using  some  substance, 
called  an  indicator,  which  is  so  acted  on  by  alkalis 
and  acids  as  to  undergo  changes  of  color,  being 
changed  one  color  by  alkalis  and  a  different  color 
by  acids.  One  substance  which  finds  wide  use  as  an 
indicator  is  a  chemical  compound  called  phenolphthal- 
cin,  a  solution  of  which  is  turned  pink  by  alkalis  and 
colorless  by  acids.  For  use  in  testing  acidity,  one  dis- 
solves 10  grams  of  the  dry  powder  in  300  cc.  of  90 
per  cent,  alcohol.  It  is  necessary  to  use  only  5  or  10 
drops  of  this  solution  as  indicator. 

GENERAL  APPLICATION  OF  PRINCIPLES  OF 
NEUTRALIZATION 

What  use  can  be  made  of  the  foregoing  facts  in 
finding  the  per  cent,  of  acid  in  a  solution?  For  sim- 
plicity, we  will  use  the  following  illustrative  experi- 
ment: In  a  glass  or  teacup  we  put  100  cc.  of  a  solu- 
tion containing  .25  per  cent,  of  lactic  acid  and  add  5 
or  10  drops  of  indicator  solution.  Into  this  mixture 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS      99 

we  run  from  a  graduated  cylinder  or  burette  some 
standard  solution  of  caustic  soda,  prepared  by  dis- 
solving- .j.  parts  by  weight  of  pure  caustic  soda  in  1,000 
parts  of  distilled  water.  This  solution  of  caustic  soda 
we  add,  a  little  at  a  time,  to  the  solution  of  lactic 
acid,  stirring  or  otherwise  agitating  the  mixture  thor- 
oughly after  each  addition.  The  pink  color  that  ap- 
pears when  the  caustic  soda  solution  is  added  disap- 
pears on  stirring.  After  the  alkali  has  been  added 
several  times,  the  color  disappears  less  rapidly  each 
time.  The  gradual  addition  of  the  alkali  is  continued 
until  finally  the  pink  color  does  not  disappear  readily 
on  continued  agitation  but  remains  for  some  moments. 
The  neutralization  of  the  acid  by  the  alkali  is  complete, 
and  the  addition  of  alkali  stops  at  this  point.  The  ap- 
pearance of  the  pink  color  throughout  the  body  of  the 
liquid  means  that  enough  alkali  has  been  added  to 
combine  with  the  lactic  acid,  and  a  little  more,  one 
drop  of  the  alkali  solution  being  enough  to  produce 
the  pink  color  with  the  indicator  after  the  acid  is  neu- 
tralized. The  liquid  in  the  cup  contained  at  the  start 
only  a  solution  of  lactic  acid.  As  soon  as  we  added 
alkali,  it  combined  with  the  lactic  acid,  forming  the 
neutral  compound,  sodium  lactate.  We  then  had  a 
mixture  of  lactic  acid  and  sodium  lactate.  As  we  con- 
tinued to  add  alkali,  the  amount  of  sodium  lactate  in- 
creased, while  the  amount  of  lactk.  acid  decreased. 
Finally,  a  point  is  reached  when  trie  solution  in  the 
cup  contains  no  free  lactic  acid,  but  only  sodium  lac- 
tate, and  the  addition  of  one  more  drop  of  alkali  turns 
the  indicator  pink,  producing  a  more  lasting  coloration 
throughout  the  solution  and  showing  that  the  acid 


100  MODERN    METHODS   OF   TESTING   MILK 

has  been  completely  neutralized,  that  is,  changed  into 
sodium  lactate. 

Having  completed  the  neutralization  of  the  acid, 
we  examine  the  burette  or  the  graduated  cylinder  con- 
taining the  alkali  to  find  exactly  how  much  alkali  so- 
lution has  been  used  in  neutralizing  the  acid.  The 
lactic  acid  has  required,  say,  28  cc.  of  soda  solution. 
Each  cubic  centimeter  of  alkali  neutralized  by  acid 
corresponds  to  .009  gram  of  acid,  and  28  cc.  would 
therefore  correspond  to  .25  gram  of  lactic  acid.  This 
amount  of  lactic  acid  in  100  cc.  is  .25  per  cent.  The 
process  of  making  a  chemical  determination  by  means 
of  a  standard  solution  is  known  as  titration. 

NEUTRALIZATION  METHOD  APPLIED  TO  TEST- 
ING ACIDITY  OF  MILK  AND  MILK  PRODUCTS 

In  practical  dairy  work,  one  is  freed  from  the  ne- 
cessity of  preparing  standard  solutions,  except  in  a 
simple  way,  and  the  calculations  needed  to  figure  the 
results  are  direct  and  easy.  The  caustic  soda  solution 
is  prepared  in  such  strength  that  a  certain  amount  of 
it  equals  .1  per  cent,  of  lactic  acid,  when  a  certain 
amount  of  milk  or  other  substance  is  used.  All  tests 
for  the  acidity  of  milk  and  its  products  are  based  upon 
the  general  principles  previously  described  and  differ 
from  one  another  simply  in  some  of  the  details  of 
carrying  out  the  process.  There  are  now  available  sev- 
eral forms  of  so-called  acid  tests,  among  which  we 
shall  describe  the  following :  "Mann's  acid  test,"  "Far- 
rington's  alkaline-tablet  test,"  and  the  "Purdue  alkali 
test." 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS    IOI 

DESCRIPTION  OF  MANN'S  ACID  TEST 

Apparatus  and  materials. — The  apparatus  and  ma- 
terials used  in  this  test  are :  ( I )  A  50  cc.  glass  burette, 
with  stopcock,  (2)  a  50  cc.  pipette  for  measuring  sam- 
ples, (3)  a  glass  beaker  and  stirring- rod,  (4) 
an  alcoholic  solution  of  phenolphthalein, 
and  (5)  a  standardized  alkali  solution  la- 
beled "neutralizer,"  each  cubic  centimeter 
of  which  contains  enough  sodium  hydrox- 
ide (.004  gram)  to  neutralize  .009  gram 
of  lactic  acid.  The  outfit  is  shown  in  Fig. 

37- 

Operating    the    test. — (i)     Measuring 
sample. — Into  a  clean  beaker  or  white  por- 
celain   cup,    one    measures 
with  the  pipette  exactly  50 
cc.   of  the  material    (milk, 
cream,   etc.)    to   be   tested. 
The  pipette  is  then  rinsed 
by  filling  with  water,  pre-       FIG   37_MANN's  ACID  TEST 
ferably    distilled,    and   this 
rinsing  water  is  added  to  the  sample. 

(2)  Adding  alkali. — The  indicator  (5  or  10  drops) 
is  then  added  to  the  sample.  The  burette  is  then  filled 
to  the  zero  mark  with  the  neutralizer,  and  some  of  it 
is  run  into  the  sample  in  the  beaker  or  cup.  A  pink 
color  appears,  but  disappears  on  stirring.  The  addi- 
tion of  alkali  in  portions  is  continued  with  care,  the 
sample  being  stirred  after  each  addition.  It  will  be 
noticed  sooner  or  later,  according  to  the  amount  of 
acid  present,  that,  after  each  addition  of  alkali,  the 


IO2  MODERN    METHODS    OF    TESTING    MILK 

pink  color  disappears  more  slowly,  showirg  that  the 
acid  is  becoming  more  nearly  neutralized.  When  the 
color  disappears  quite  slowly,  the  neutralizer  should 
be  added  a  drop  at  a  time.  Finally  a  point  is  reached 
when,  after  the  addition  of  one  drop  of  alkali,  the 
pink  color  does  not  disappear  even  after  stirring  10 
or  15  seconds.  This  indicates  that  the  acid  is  com- 
pletely neutralized.  Add  no  more  alkali.  The  pink 
color  will  slowly  disappear  after  standing  some  time, 
even  when  the  solution  is  alkaline.  Some  experience 
enables  one  easily  to  know  when  the  pink  color  is  suf- 
ficiently permanent. 

(3)  Calculating  results. — Having  completed  the  ad- 
dition of  alkali,  the  burette  is  examined  to  see  how 
many  cubic  centimeters  of  neutralizer  have  been  used. 
The  percentage  of  acid  for  50  cc.  or  any  amount  of 
sample  taken  is  calculated  from  the  following  for- 
mula : 


Per  cent  of  acid=^0-  cc'  °f  alkalj  x  -°°9  xioo. 
No.  cc.  of  sample  taken 


When  one  uses  50  cc.  of  the  sample,  this  formula 
becomes 

Per  cent,  of  acid  =  No.  cc.  of  alkali  X  .018. 

From  this  last  formula  one  can  prepare  a  table  which 
gives  the  results  and  saves  making  calculations  at 
every  test: 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS    IC»3 


C.C.  OF  ALKALI  SOLUTION 
(NEUTRALIZER)  USED 

Per  cent,  of  acid 
in  sample  tested 
018 

2                            

036 

? 

054 

072 

c 

09 

JO                     

18 

1C 

27 

2O                                                                   . 

.36 

-2Q 

.54 

40,    etc.           

72,    etc. 

By  using  the  first  formula  above,  similar  tables  can 
be  prepared  when  the  amount  of  sample  taken  is  any 
amount  other  than  50  cc. 

Using  Babcock  Pipette  with  Mann's  Test.  —  If  a 
17.6  cc.  pipette  is  used  in  measuring  the  liquid  to  be 
tested,  the  percentage  of  acid  may  be  found  by  divid- 
ing by  2,  the  number  of  cubic  centimeters  of  Mann's 
alkali  used,  the  result  being  expressed  as  tenths  per 
cent.  Thus,  if  the  liquid  tested  neutralizes  13  cc.  of 
alkali,  the  acidity  is  13  divided  by  2,  which,  expressed 
as  tenths,  is  .65  per  cent.  By  diluting  Mann's  "neutral- 
izer"  with  an  equal  volume  of  water,  the  number  of 
cubic  centimeters  gives  directly  the  percentage  of  acid- 
ity, expressed  as  tenths. 

FARRINGTON'S  ALKALINE-TABLET    TEST 

Apparatus  and  materials.  —  In  this  method  the 
same  chemical  principles  are  employed  as  in  Mann's 
test,  but  the  alkali,  in  the  form  of  a  carbonate,  and  in- 
dicator are  mixed  together  in  the  form  of  solid  tab- 
lets. Each  tablet  contains  enough  alkali  to  neutralize 


-    104  MODERN    METHODS   OF   TESTING   MILK 

.034  gram  of  lactic  acid.  The  apparatus  (Fig.  38) 
consists  of  a  17.6  cc.  pipette,  a  white  porcelain  cup,  and 
a  100  cc.  graduated  glass  cylinder  provided  with  a 
rubber  stopper. 

Preparing  the  alkali  solution.  —  In  using  the  alka- 
line tablets,  one  first  puts  5  tablets  into  the  graduated 

100  cc.  cylinder,  and  fills 
this  to  the  97  cc.  mark  with 
clean,  soft  water,  prefera- 
bly distilled.  The  cylinder 
is  then  tightly  corked  and 
laid  on  its  side  until  the 
tablets  dissolve,  which  re- 
quires several  hours.  The 
FIG.  38-FARRiNGTON's  cylinder  must  be  kept 

ALKALINE-TABLET   TEST 


none  of  the  solution  can  be  lost  while  the  tablets  are 
dissolving.  A  slight  flocculent  residue  will  not  dis- 
solve, consisting  of  some  inert  matter  used  in  the  mak- 
ing of  the  tablets. 

Precautions  in  using  alkali  solution.  —  The  solu- 
tion should  always  be  shaken  well  before  using.  It 
should  always  be  kept  tightly  stoppered  when  not  in 
use.  The  solution,  if  kept  perfectly  stoppered,  will 
not  greatly  change  in  a  week.  Solutions  older  than 
this  may  change  their  strength  and  should  not  be  used. 
It  is  a  wise  precaution  to  throw  away  solutions  previ- 
ously used  for  some  days  and  to  prepare  a  fresh  solu- 
tion. The  solid  tablets  do  not  change  if  kept  dry. 

Operation  of  alkaline-tablet  test.  —  The  material 
(milk,  cream,  etc.)  to  be  tested  is  thoroughly  mixed, 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS    IO5 


and  17.6  cc.  is  then  measured  into  a  clean  porcelain 
cup  with  a  pipette.  The  pipette  is  rinsed  by  filling  with 
water,  which  is  added  to  the  sample  in  the  cup.  The 
tablet  solution  prepared  in  the  manner  described  is 
poured  slowly  into  the  cup  in  small  portions  at  a  time, 
and  the  mixture  is  agitated  by  rotating  the  cup  after 
each  addition  of  alkali.  When  the  pink  color  does  not 
disappear  readily  on  agitating  (p.  102),  the  number  of 
cubic  centimeters  of  alkali  used  is  read  from  the  grad- 
uated cylinder.  Each  cubic  centimeter  of  alkaline-tab- 
let solution  used  equals  .01  per  cent,  of  lactic  acid  in 
the  sample  tested.  For  example,  the  use  of  25  cc.  of 
alkali  solution  equals  .25  per  cent,  of  acid;  40  cc. 
equals  .40  per  cent.,  etc. 

SPILLMAN'S    MODIFICATION    OF 
ALKALINE-TABLET    TEST 

The  apparatus  consists  of  an  ordi- 
nary teacup,  a  regular  17.6  cc.  pipette, 
a  quart  Mason  fruit-jar,  and  "Spill- 
man's  acid-test  cylinder"  (Fig.  39). 
The  alkali  solution  is  prepared  by  dis- 
solving alkaline  tablets  in  water  at 
the  rate  of  5  tablets  for  one  cylinder 
of  water  filled  to  the  mark  8,  the  so- 
lution being  made  and  kept  in  the 
fruit- jar.  Observe  the  precautions 
given  above  in  using  tablet  solutions. 
In  making  the  test,  put  17.6  cc.  of  TEST  CYLINDER 
the  material  to  be  tested  in  a  teacup, 
pour  into  the  cup  the  alkali  solution  in  the  manner  de- 
scribed above,  until  the  pink  color  remains.  Then 


^ 

•—— 

FIG.  39 
SPILLMAN'S  ACID- 

IO6  MODERN    METHODS    OF    TESTING    MILK 

pour  the  contents  of  the  teacup  into  the  Spillman  cyl- 
inder and  read  the  scale  at  the  surface  of  the  liquid 
in  the  cylinder.  The  results  indicate  the  acidity  in 
tenths  of  one  per  cent.  The  cylinder  reads  as  high  as 
8  tenths. 


TABLET  TEST  MODIFIED  FOR  RAPID  ESTIMA- 
TION OF  ACIDITY 

It  is  often  desirable  to  ascertain  quickly  whether 
milk  or  cream  contains  more  or  less  than  .2  or  .3  per 
cent,  of  acid.  Farrington  and  Woll  have  devised  the 
following  method:  An  alkali  solution  is  prepared  by 
dissolving  in  an  8-ounce  bottle  2  tablets  for  each 
ounce  of  water  used.  A  No.  10  brass  cartridge  shell, 
on  which  a  wire  handle  is  soldered,  is  used  for  meas- 
uring the  sample  to  be  tested  and  also  the  alkali.  A 
cartridgeful  of  milk  or  cream,  is  placed  in  a  teacup 
and  then  a  cartridgeful  of  the  alkali  solution  is  added. 
The  contents  of  the  cup  are  mixed  by  a  rotary  motion. 
If  the  sample  tested  remains  white,  it  contains  over 
.2  per  cent,  of  acidity;  if  a  pink  color  remains,  the 
acidity  is  less  than  .2  per  cent.  The  intensity  of  the 
pink  color  indicates  the  relative  amount  of  acid  pres- 
ent, since  the  color  will  be  more  intense  in  proportion 
as  there  is  less  acid.  Any  other  measure  may  be  used 
in  place  of  the  brass  cartridge-shell,  but  in  every  case 
care  must  be  taken  to  use  equal  amounts  of  milk  or 
cream  and  of  alkali  solution. 


TESTING  ACIDITY  OF  MILK  AND  HIL.K  PRODUCTS    IOJ 

THE  PURDUE  ALKALI  TEST 

This  test  was  devised  by  H.  E.  Van  Norman  (Bul- 
letin No.  104,  Purdue  Univ.  Agr.  Exp.  Sta.,  1905.) 
The  following  apparatus  (Fig.  40)  is  used:  (i)  An 


01  LUTE  ALKALI 

SOLUTION 
ICC=X)I%  WITH 
17.6  CC     PIPETTE 
OF   CREAM    ETC. 


FIG.    40 — PURDUE   ALKALI   TEST 


ordinary  17.6  cc.  pipette,  (2)  a  100  cc.  cylinder,  such 
as  is  used  in  the  alkaline-tablet  test, (3)  a  2-quart  bot- 
tle graduated  at  1850  cc.,  (4)  sealed  bottles,  each  con- 
taining 37  cc.  of  normal  solution  of  sodium  hydroxide 
(caustic  soda),  (5)  a  bottle  of  phenolphthalein  indi- 


IO8  MODERN    METHODS   OF  TESTING   MILK 

cator  and  (6)  an  ordinary  white  teacup.  The  alkali 
solution  must  be  of  guaranteed  accuracy  and  should 
be  obtained  only  from  a  reliable  chemical  or  dairy- 
supply  house. 

The  test  is  conducted  as  follows :  Into  the  1850  cc. 
bottle  one  empties  the  small  bottle,  containing  37  cc. 
of  normal  alkali  solution,  rinsing  the  small  bottle  with 
water  once  or  twice  and  adding  the  rinsings  to  the 
large  bottle,  which  is  then  filled  to  the  mark  with  wa- 
ter. Use  only  clean,  soft  or,  preferably,  distilled  wa- 
ter. This  large  bottle  is  kept  tightly  stoppered.  Meas- 
ure into  a  white  teacup  17.6  cc.  of  the  material  to  be 
tested,  rinse  the  pipette  with  clean  water,  adding  the 
rinse  water  to  the  sample  in  the  cup,  and  then  add 
5  or  10  drops  of  indicator.  From  the  graduated  cyl- 
inder, filled  to  the  100  cc.  mark  with  the  dilute  alkali 
solution,  one  pours  the  solution  in  portions  into  the 
sample  to  be  tested,  agitating  after  each  addition  of 
alkali,  and  continuing  the  addition  of  alkali  solution 
until  the  pink  color  does  not  disappear  on  agitation. 
Then,  from  the  cylinder  read  the  number  of  cubic  cen- 
timeters of  alkali  used.  Each  cubic  centimeter  corre- 
sponds to  .01  per  cent  of  acid. 

COMPARISON  OF  DIFFERENT  FORMS  OF 
ACID  TESTS 

Mann's  acid  test  has  the  advantage  of  furnishing 
the  alkaline  solution  ready  for  use  at  any  time.  It 
has  this  serious  disadvantage,  that  the  alkaline  solu- 
tion is  in  constant  danger  of  becoming  weakened  by 
absorption  of  carbon  dioxide  when  exposed  to  the  air. 
A  weakened  alkali  solution  gives  higher  results  of 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS    IOO, 

acidity  than  the  truth.  It  has  also  the  disadvantage  of 
requiring  a  calculation  to  obtain  the  results  in  the 
form  of  per  cent.,  and  any  other  form  of  statement 
ought  not  to  be  used. 

The  alkaline-tablet  test  has  the  advantage  of  giving 
the  results  directly  in  percentages.  The  tablets  do  not 
change  if  kept  dry,  and  the  use  of  a  fresh  solution 
avoids  all  uncertainity  of  strength.  The  cost  of  trans- 
portation is  insignificant  compared  with  that  of  the 
neutralizer.  The  tablets  are  not  always  absolutely 
uniform  in  strength  of  alkali,  but  the  variations  are 
not  sufficient  to  make  serious  differences  in  results. 

In  the  Purdue  modification,  the  small  bottles  of  al- 
kali do  not  lose  strength  so  long  as  they  are  kept 
properly  stoppered,  and  therefore  any  number  can  be 
ordered  at  a  time.  Being  more  concentrated  than 
Mann's  neutralizer,  the  cost  of  transportation  is  less. 
The  solution  is  more  quickly  and  conveniently  prepared 
than  the  tablet  solution.  The  strength  of  the  small 
bottles  of  alkali  is  said  to  be  more  strictly  uniform  than 
in  the  case  of  tablets.  By  high  dilution  of  the  alkali 
solution  when  used,  the  chance  of  error  is  reduced. 

TESTING  THE  ACIDITY  OF  WHEY 

Whey  may  be  tested  by  any  of  the  methods  de- 
scribed. Owing  to  the  comparatively  low  acidity  of 
whey  in  the  operation  of  cheese-making,  it  is  desirable 
either  to  have  the  alkali  dilute  ( i  cc.  of  alkali  equal  to 
.01  per  cent,  acid),  or  else  to  take  twice  as  much  whey 
for  testing  as  in  the  case  of  cream,  the  final  results 
being  corrected  by  dividing  by  2.  The  whey  should 
be  free  from  particles  of  curd,  since  curd  has  the 


IIO  MODERN    METHODS    OF    TESTING    MILK 

power  of  neutralizing  alkali  to  some  extent.  The  per- 
centage of  acid  in  milk  can  be  used  as  a  guide  in 
ripening  the  milk  before  adding  rennet,  in  the  rate  of 
heating  (cooking)  the  curd,  in  the  regulation  of  the 
piling  of  the  curd,  in  the  time  of  milling,  etc. 

TESTING  THE  ACIDITY  OF  CHEESE 
From  a  sample  of  cheese,  prepared  in  the  manner 
described  on  page  8):,  weigh  nine  grams  and  to  this 
add  water  at  a  temperature  of  100°  to  110°  F.  until 
the  volume  equals  90  to  100  cc.  Agitate  vigorously 
and  filter.  To  the  filtrate  add  alkali  solution,  each 
cubic  centimeter  of  which  equals  .01  per  cent,  of  lac- 
tic acid,  carrying  out  the  test  as  with  milk,  cream,  etc. 
The  number  of  cubic  centimeters  of  alkali  used,  mul- 
tiplied by  2,  equals  the  per  cent,  of  acid  in  the  cheese. 
Much  higher  results  are  obtained  if  one  treats  the 
cheese  instead  of  its  water  extract  with  alkali,  because 
the  nitrogen  compounds  of  the  cheese  neutralize  alkali. 

RELATION  OF  FAT  IN  CREAM  TO  ACIDITY  OF 
CREAM-RIPENING 

Cream  rich  in  fat  ripens,  that  is,  becomes  acid,  more 
slowly  than  cream  poor  in  fat.  This  is  so,  because  the 
larger  the  percentage  of  fat  in  cream  the  smaller  is 
the  percentage  of  sugar,  and  the  sugar  is  the  source  of 
lactic  acid.  The  favorable  influence  of  ripening  upon 
the  process  of  churning  is  believed  to  be  due  to  the 
action  of  the  acid  upon  the  calcium  casein  of  the  cream, 
converting  it  into  calcium  lactate  and  so  lessening  its 
tenacious  hold  upon  the  fat-globules  in  emulsion.  The 
fat  itself  of  the  cream  is  not  changed.  The  amount 


TESTING  ACIDITY  OF  MILK  AND  MILK  PRODUCTS    III 

of  acid  to  be  formed  in  cream-ripening  is,  therefore,  to 
be  governed  more  by  the  amount  of  calcium  casein  in 
the  cream  than  by  any  other  constituent.  The  less  fat 
there  is  in  normal  cream,  the  more  casein  there  will  be, 
and  the  greater  the  per  cent,  of  acidity  needed.  The 
more  fat  there  is  in  cream,  the  less  calcium  casein  there 
will  be,  and  the  less  the  amount  of  acid  needed.  These 
statements  conform  to  practical  experience.  Thus, 
it  is  found  that  in  cream  containing  25  per  cent,  of 
fat,  it  is  necessary  to  produce  nearly  .7  per  cent,  of 
acid  in  order  to  get  the  results  sought  by  ripening, 
while,  in  cream  containing  35  per  cent,  of  fat,  less 
than  .6  per  cent,  of  acid  is  sufficient. 

To  ascertain  how  much  acid  should  be  formed  in 
cream  before  churning,  the  following  rule  is  suggested 
by  Van  Norman  (Bulletin  104,  Purdue  Univ.  Agr. 
Exp.  Sta.)  :  From  100  substract  the  per  cent,  of  fat 
in  the  cream  tested  and  multiply  the  result  by  .9,  or, 
expressed  as  a  formula,  (100  —  per  cent,  of  fat  in 
cream )x«9.  For  example: 

Cream  with  20  per  cent,  fat  requires  .72  per  cent,  of 
acidity. 

Cream  with  25  per  cent,  fat  requires  .67  per  cent,  of 
acidity. 

Cream  with  30  per  cent,  fat  requires  .63  per  cent,  of 
acidity. 

Cream  with  35  per  cent,  fat  requires  .58  per  cent,  of 
acidity. 

The  use  of  .9  as  a  factor  for  multiplying  may  not 
suit  all  conditions  and  some  other  factor,  .8  for  exam- 
ple, may  be  used.  Each  operator  may  experiment  and 


112  MODERN    METHODS    OF   TESTING    MILK 

easily  find  what  per  cent,  of  acidity  is  best  adapted  to 
the  production  of  the  butter  suiting  his  market,  and 
then  a  table  like  the  above  can  be  made,  using  .9  or 
some  other  factor. 

OUTLINE  STATEMENT   OF  SOME  SPECIAL 
PRECAUTIONS  IN  TESTING  ACIDITY 

1.  The  material  to  be  tested   for  acidity  must  be 
thoroughly  mixed  before  sampling  for  a  test. 

2.  The  water  used  in  preparing  the  alkali  solution 
and  in  rinsing  the  pipette  should  be  neither  acid  nor 
alkaline  and  should  be  soft  and  clean.     Use  distilled 
water  if  possible. 

3.  The  alkaline  tablets  should  be  kept  dry  in  well- 
stoppered  bottles. 

4.  The  alkali  solution,  in  whatever  form  used,  must 
be  kept  from  contact  with  the  air  as  much  as  possible 
to  prevent  changing  strength  either  through  evapora- 
tion or  absorption  of  carbon  dioxide. 

5.  When  alkaline  tablets  are  used,  prepare  a  fresh 
solution  in  order  to  be  sure  of  its  strength,  if  there  is 
any  reason  for  uncertainty. 

6.  The  tests  should  be  made  in  a  good  light  so  that 
one  can  easily  see  the  appearance  of  the  longer-lasting 
pink  color  at  the  end  of  the  reaction. 

7.  The  appearance  of  the  pink  color  at  the  end  of 
the  test  can  usually  be  more  sharply  seen  by  diluting 
the  material  examined  with  three  or  four  times  its  vol- 
ume of  distilled  water. 


CHAPTER   VIII 

Method  of  Testing  the  Bacterial  Condition  of 

Milk 

A  thorough  bacteriological  examination  of  milk  re- 
quires somewhat  extended  special  training,  but  there 
are  methods  for  ascertaining  the  general  bacterial  con- 
dition of  milk  which  are  available  in  the  hands  of  any 
careful  worker,  and  which  afford  most  valuable  sug- 
gestions in  regard  to  the  cleanliness  of  milk.  The 
methods  of  studying  the  bacterial  condition  of  milk 
which  we  shall  notice  are  (i)  determining  the  acidity, 
(2)  the  fermentation  method  known  in  its  most  avail- 
able form  as  the  "Wisconsin  Curd-Test,"  and  (3)  test- 
ing for  dirt  in  suspension. 

THE   RELATION    OF  ACIDITY   TO   THE  BACTE- 
RIAL CONDITION  OF  MILK 

The  details  of  the  method  of  determining  acidity  in 
milk  have  been  given  in  Chapter  VII.  We  need  say 
here  only  a  few  words  in  regard  to  the  interpretation 
of  the  results  as  they  relate  to  the  cleanly  character 
of  milk  and  its  fitness  for  use.  The  amount  of  acid  in 
milk  is  generally  an  indication  of  the  care  given  to  the 
milk  after  being  drawn  from  the  cow ;  to  some  extent, 
it  indicates  the  age  of  the  milk,  especially  if  the  tem- 
perature at  which  it  has  been  kept,  is  known ;  and,  if 
the  age  of  the  milk  is  known,  the  acidity  indicates,  to 
some  extent,  the  temperature  at  which  the  milk  has 

113 


114  MODERN    METHODS   OF   TESTING    MILK 

been  kept.  The  cleanliness  of  the  milk-pails  and  other 
vessels  and  utensils  with  which  the  milk  comes  in  con- 
tact is  another  important  factor  in  influencing  acidity. 
The  average  acidity  of  English  market  milk,  sup- 
posed to  be  12  to  18  hours  old,  is  .18  per  cent,  and  of 
German  milk,  .13  to  .18  per  cent.  Market  milk  should 
not,  in  any  case,  contain  over  .2  per  cent  of  total  acid- 
ity when  it  reaches  the  consumer,  and  should  generally 
be  under  .15  per  cent.  This  (.2  per  cent.)  is  also  the 
highest  limit  allowable  for  milk  that  is  to  be  used  for 
cheese-making.  The  test  for  acidity  can  thus  be  made 
a  very  useful  indication  of  the  bacterial  condition  of 
milk  so  far  as  it  relates  to  the  acidity,  and  to  the 
abundance  of  those  forms  that  produce  lactic  acid. 

THE   FERMENTATION    OR   WISCONSIN 
CURD-TEST 

Milk  frequently  contains  objectionable  forms  of 
organisms  or  ferments  that  are  not  made  perceptible 
by  ordinary  methods  of  observation.  The  condition 
arises  particularly  in  milk  used  for  cheese-making  and 
may  result  in  serious  injury  to  the  quality  of  the  cheese. 
The  Wisconsin  Experiment  Station  (Wis.  £xp.  Sta. 
I2th  and  I5th  Annual  Reports,  1895  and  1898)  has 
applied  certain  principles  to  the  development  of  a 
test  that  enables  one  to  identify  milk  containing  cer- 
tain forms  of  undesirable  ferments  likely  to  do  serious 
injury.  This  method  is  based,  in  general,  upon  the 
plan  of  making  conditions  favorable  for  the  rapid  de- 
velopment of  the  ferments  present  in  milk. 

Apparatus. — The  apparatus  consists  of  the  follow- 
ing parts:  (i)  Pint  glass  jars  or  tin  cans  with  covers; 


TESTING   THE    BACTERIAL    CONDITION    OF    MILK    115 

(2)  a  well  insulated  tank  to  hold  the  jars,  (3)  rennet 
extract,  (4)  a  thermometer,  (5)  a  case-knife  or  simi- 
lar instrument  for  cutting  curd,  and  (6)  a  small  pipette 
for  measuring  rennet-extract. 

Operation  of  test. — The  test  is  conducted  as  fol- 
lows: The  jars,  including  covers,  just  previous  to 
use,  are  sterilized  with  live  steam,  scalding  water  or 
dry  heat  (212°  F.).  Each  jar  or  can  is  rilled  about 
two-thirds  full  with  the  milk  to  be  tested  and  the  ster- 
ilized cover  put  on  at  once.  The  jars  are  then  placed 
in  the  tank  which  is  rilled  with  water  at  100°  to  102° 
F.  up  to  the  upper  surface  of  the  milk  in  the  jars.  The 
temperature  of  the  water  should  be  kept  at  100°  to 
102°  F.  during  the  whole  operation.  To  hasten  the 
warming  of  the  milk,  the  jars  are  taken  out  and  shaken 
occasionally.  The  temperature  of  the  milk  is  observed 
with  a  sterile  thermometer,  and  when  the  milk  has 
reached  98°  F.,  one  adds  10  drops  of  rennet-extract 
to  each  jar  and  mixes  thoroughly  by  giving  the  con- 
tents of  the  jar  a  rotary  motion.  When  the  milk  has 
coagulated,  it  is  allowed  to  stand  until  it  is  firm,  usu- 
a!ly  about  20  minutes.  To  enable  the  whey  to  sepa- 
rate more  readily,  the  curd  is  then  cut  fine  with  a 
thin  knife,  which  must  be  carefully  rinsed  with  hot 
water  after  finishing  each  jar  and  before  using  it  in 
another,  in  order  to  avoid  carrying  contamination  from 
one  milk  to  another  and  spoiling  the  test.  The  curd 
is  allowed  to  settle  completely.  When  the  whey  has 
been  separating  half  an  hour,  the  samples  are  exam- 
ined for  flavor  by  smelling,  after  which  the  whey 
is  carefully  poured  out  of  the  jars  and  this  is  re- 


Il6  MODERN    METHODS   OF   TESTING    MILK 

peated  at  intervals  of  30  to  40  minutes  for  8  hours 
or  more.  Under  the  favorable  conditions  of  tempera- 
ture, similar  to  those  employed  in  cheese-making,  the 
organisms  present  develop  readily  and  reveal  their 
presence  in  different  characteristic  ways.  The  jars 
are  finally  opened,  any  whey  present  is  drained  off, 
and  the  following  tests  are  applied:  (i)  The  curd  is 
cut  into  two  pieces.  The  curd  will  be  solid  and  free 
from  holes  on  the  cut  surfaces,  if  the  milk  is  not 
tainted.  If  it  is  spongy  and  full  of  holes,  it  con- 
tains those  undesirable  organisms  that  produce  gases 
in  the  curd  and  injure  it  for  cheese-making,  showing 
in  the  form  of  "floating  curds"  and  "huffy"  cheese. 
The  holes  are  usually  small,  their  common  name  be- 
ing "pin-holes."  (2)  The  curd  is  examined  with  ref- 
erence to  any  marked  disagreeable  odors  that  may 
be  present.  Some  undesirable  organisms  reveal  their 
presence  by  smell  without  making  spongy  curd.  This 
may,  perhaps,  be  best  perceived  by  smelling  of  a 
freshly  cut  surface  of  the  curd.  Offensive  odors  are, 
of  course,  an  undesirable  indication.  Special  appara- 
tus for  performing  the  test  is  furnished  by  dairy-sup- 
ply houses,  but  pint  fruit-jars  and  other  home-made 
appliances  will  answer  satisfactorily. 

By  this  method  one  can  learn  what  particular  lot 
of  milk  among  several  is  responsible  for  undesirable 
fermentations.  Moreover,  having  traced  the  source  of 
contamination  to  a  single  herd  of  cows,  it  is  easily 
possible,  by  applying  the  test  to  single  cows,  to  ascer- 
tain which  individual  or  individuals  may  be  the  source 
of  trouble. 


TESTING   THE   BACTERIAL    CONDITION    OF    MILK    117 

Precautions. — Two  points  must  be  carefully  ob- 
served in  carrying  out  this  test :  ( i )  The  temperature 
must  be  kept  as  near  98°  F.  as  possible,  in  order  that 
the  bacteria  may  develop  as  desired.  This  can  be 
done  by  keeping  the  temperature  of  the  water  sur- 
rounding the  jars  at  100°  to  102°  F.  The  tempera- 
ture must  be  watched.  (2)  The  thermometer  and  the 
knife  used  should  be  made  not  only  clean  but  sterile 
each  time  after  using  in  one  sample  before  placing 
them  in  another. 

GERBER'S  FERMENTATION  TEST 

This  test  consists  in  heating  milk  in  tubes  6  hours 
at  104°  to  106°  F.  and  then  observing  the  odor,  ap- 
pearance, taste,  etc.,  for  abnormal  qualities.  The  milk 
is  heated  a  second  time  for  6  hours  at  104°  to  106°  F. 
Any  abnormal  coagulation  of  the  milk  is  noticed,  such 
as  holes  due  to  gas,  Gerber  states  that  milk  coagu- 
lating in  less  than  12  hours  is  abnormal,  due  either 
to  the  abnormal  character  of  the  milk  itself  when 
drawn  or  to  improper  care  after  being  drawn.  Milk 
that  does  not  curdle  within  24  to  48  hours  is  open  to 
the  suspicion  of  containing  preservatives  and  should 
be  examined  for  such  substances. 

METHOD   OF  TESTING  MILK  FOR   SUSPENDED 
DIRT 

The  amount  of  dirt  in  suspension  in  milk  can  be 
estimated  without  serious  difficulty.  The  best  way  is 
to  provide  a  small  centrifugal  machine  that  is  made 
to  run  at  higher  speed  than  the  Babcock  tester.  A 


MODERN    METHODS   OF   TESTING    MILK 

form  of  hand-centrifuge  is 
shown  in  Fig.  41.  Special 
graduated  tubes  (Fig.  42) 
are  made  to  use  in  this.  The 
milk  to  be  tested  is  stirred 
thoroughly,  the  tube  is  filled 
to  the  highest  mark,  placed 
in  the  pocket  of  the  centri- 
fuge and  whirled  several 
minutes.  The  sediment  col- 
lects at  the  bottom  and  can 
be  easily  measured  by  read- 
ing the  amount  on  the  scale. 
In  Fig.  43  is  shown  a  Bausch 
and  Lomb  electric  centrifuge. 
This  company  also  furnishes 
hand-centrifuges  capable  of 

FIG.   41 — HAND-CENTRIFUGE  .     .. 

FOR  SEDIMENTATION  WORK    3>ooo  to  8,ooo  revolutions  per 


FIG.    42 — TUBE   FOR 
SEDIMENTATION    WORK 


FIG.   43 — BAUSCH    &  LOMB 

ELECTRIC  CENTRIFUGE 
Speed  1,000  revolutions  per  minute 


I2O  MODERN    METHODS    OF   TESTING    MILK 

minute.  Their  centrifuges  and 
tubes  can  be  used  also  in  testing 
for  fat  in  milk  by  the  Babcock 
method.  In  Fig.  44  is  shown 
another  form  of  electrical  cen- 
trifuge which  is  very  satisfactory 

FIG.  45  for  collecting  sediments. 

J?R  COLLECTING       A  .method   less   accurate,   but 

M.kNT     IN     MILIv 

fairly  satisfactory  in  the  absence 
of  any  better  means,  is  to  place  about  4  ounces  of  milk 
in  a  test-glass  (Fig.  45)  and  let  it  stand  for  one  or 
two  hours.  The  dirt  collects  in  the  bottom  and  its 
amount  can  be  roughly  estimated  by  the  eye. 


CHAPTER    IX 

Methods  of  Testing  Milk  by  Rennet- Extract 
and  Pepsin 

In  cheese-making  it  is  necessary  to  have  some  means 
of  finding  out  when  the  rennet-extract  should  be  ad- 
ded to  milk  in  order  to  secure  the  best  results  in  the 
process.  This  is  usually  known  as  "testing  the -ripe- 
ness of  milk."  Two  methods  are  in  common  use  for 
this  purpose:  (i)  The  Monrad  test  and  (2)  the 
Marschall  test. 

THE  MONRAD  TEST 

This  test  is  based  upon  the  amount  of  time  re- 
quired for  a  definite  quantity  of  milk  at  a  given  tem- 


FIG.    46 — MONRAD  RENNET-TEST 

perature  to  become  coagulated  by  a  fixed  quantity  of 
rennet. 

The  pieces  of  apparatus  (Fig.  46)  required  are  the 
following:  (i)  A  tin  cylinder  for  measuring  milk, 
holding,  when  full,  160  cc.,  (2)  a  5  cc.  pipette,  (3)  a 

i2T 


122  MODERN    METHODS    OF   TESTING    MILK 

50  cc.  glass  flask,  (4)  a  thermometer,  and  (5)  a  half- 
pint  tin  basin. 

In  testing  the  ripeness  of  milk  by  means  of  rennet- 
extract,  one  first  prepares  a  dilute  solution  of  the 
rennet,  as  follows:  One  measures  with  the  small  pi- 
pette 5  cc.  of  rennet-extract  into  the  50  cc.  flask.  The 
pipette  is  then  rinsed  twice  with  water  by  sucking  it 
full  of  cold,  clean  water  to  the  mark,  the  rinsings  also 
being  run  into  the  50  cc.  flask.  The  flask  is  then  filled 
with  water  to  the  50  cc.  mark,  and  the  contents  are 
well  mixed  by  shaking.  The  next  step  is  to  fill  the 
tin  cylinder  with  the  well-mixed  milk  to  be  tested  and 
this  is  emptied  into  the  half-pint  basin.  The  milk 
must  be  at  the  temperature  at  which  one  adds  the 
rennet  in  cheese-making,  which  is  generally  about  85° 
or  86°  F.  To  the  milk  at  the  desired  temperature,  one 
adds  5  cc.  of  the  diluted  rennet  solution,  mixes  it 
through  the  milk  quickly,  using  the  thermometer  as 
a  stirrer.  The  exact  time  when  the  rennet-extract  is 
added  to  the  milk  is  noted  by  the  second-hand  of  a 
watch  and  then  again  when  the  milk  has  coagulated; 
the  number  of  seconds  required  to  coagulate  the  milk 
is  recorded.  The  exact  point  of  coagulation  can  be 
seen  more  sharply  by  scattering  a  few  particles  of 
charcoal  (as  the  blackened  end  of  a  partly  burned 
match)  on  the  surface  of  the  milk,  and  then  with  the 
thermometer  starting  the  surface  into  motion  around 
the  dish.  The  black  particles  stop  the  instant  the 
milk  coagulates.  By  using  a  stop-watch,  great  accu- 
racy and  delicacy  can  be  attained.  Care  should  be 
taken  to  keep  the  temperature  of  the  milk  at  85°  or 
86°  F.,  testing  frequently  with  the  thermometer;  and, 


TESTING  MILK  BY  RENNET-EXTRACT  AND  PEPSIN  123 


in  case  the  temperature  drops,  it  can  be  raised  by  plac- 
ing the  basin  of  milk  in  warm  water.  In  ordinary 
cheddar  cheese-making,  milk  is  ready  for  the  addition 
of  rennet  when  it  coagulates  in  30  to  60  seconds  un- 
der the  foregoing  conditions. 

THE  MARSCHALL  TEST 

In  this  test  the  same  general  procedure  is  followed 
as  in  the  Monrad  test,  but  the  rate  of  coagulation  is 
observed  in  a  different  way.  The  following  pieces  of 
apparatus  (Fig.  47)  are 
used:  (a)  A  testing  cup 
or  basin,  of  about  a  pint 
capacity,  for  holding  the 
milk  to  be  tested.  On  the 
inside  wall  of  this  cup  there 
are  graduated  spaces  be- 
ginning with  zero  at  the 
top  and  going  by  half-divis- 
ions to  7  near  the  bottom 
of  the  cup,  while  in  the  bot- 
tom of  the  cup  is  a  glass 
tube  with  a  very  small  bore, 
(b)  An  ounce  bottle  with  a  mark  on  it  to  indicate  20 
cc.  (c)  A  spatula  for  stirring  the  milk,  (d)  A  I  cc. 
pipette. 

The  operation  of  conducting  this  test  is  as  follows: 
Measure  with  the  pipette  I  cc.  of  the  rennet-extract 
used  and  empty  it  into  the  ounce  bottle,  previously 
half  rilled  with  clean  cold  water.  Rinse  the  pipette 
two  or  three  times  by  drawing  water  into  it  from  the 
bottle  and  allowing  it  to  run  back  into  the  bottle.  Mix 
well  by  shaking.  Then  place  the  milk  to  be  tested 


FIG.  47 
MARSCHALL  RENNET-TEST 


124  MODERN    METHODS   OF   TESTING    MILK 

in  the  test-cup,  setting  it  in  a  level  position  and  allow- 
ing the  milk  to  run  out  at  the  bottom.  Taking  the  bot- 
tle of  diluted  rennet  in  one  hand  and  the  spatula  in 
the  other,  watch  the  level  of  the  milk  in  the  cup.  The 
moment  the  upper  surface  of  the  milk  drops  to  the 
zero  mark,  pour  the  diluted  rennet  into  the  milk  and 
stir  well.  Then  leave  it  alone.  When  the  milk  coagu- 
lates, it  stops  running  through  the  glass  tube.  From 
the  graduated  scale,  read  the  number  of  spaces  un- 
covered on  the  inside  of  the  cup,  showing  how  many 
divisions  of  milk  have  run  out.  The  more  slowly  the 
milk  coagulates,  the  larger  the  amount  that  runs  out; 
the  more  quickly  the  milk  coagulates,  the  smaller  the 
amount  that  runs  out  and  the  fewer  spaces  there  are 
uncovered.  When  about  2^  spaces  are  uncovered, 
the  milk  is  ready  for  addition  of  rennet.  The  tempera- 
ture must  be  watched,  being  tested  at  the  start  and 
finish,  especially  in  a  cold  room. 

Some  objectionable  features  of  the  Marschall  test 
should  be  noticed.  A  difference  in  the  size  of  the  bore 
of  the  glass  tube  in  the  bottom  of  the  cup  obviously 
makes  a  difference  in  the  results.  It  is  found  that  the 
size  of  the  bore  of  the  glass  tubing  varies  in  different 
cups.  Therefore,  the  results  given  by  one  cup  can  not 
be  compared  with  those  of  another,  unless  they  arc 
tested  on  the  same  milk  and  found  to  agree.  Special 
pains  must  be  taken  to  keep  the  tube  open,  since  a  lit- 
tle dirt  quickly  stops  it.  The  Marschall  test  is  con- 
venient for  ordinary  work,  but  is  not  capable  of  as 
great  delicacy  as  is  the  Monrad  test.  Results  obtained 
by  different  workers  can  be  compared  by  the  Monrad 
test,  but  not  by  the  Marschall  test. 


TESTING  MILK  BY  RENNET-EXTRACT  AND  PEPSIN   12 j 

METHOD  OF  TESTING  RENNET-EXTRACTS 

Rennet-extract  is  prepared  by  soaking  calves'  stom- 
achs in  dilute  brine.  This  treatment  dissolves  from 
the  mucous  membrane  the  enzym  or  chemical  ferment 
that  has  the  property  of  coagulating  milk-casein,  a 
property  upon  which  the  process  of  cheese-making  is 
dependent.  The  ferment  contained  in  rennet-extracts 
appears  to  be  the  same  as  pepsin  in  regard  to  its  ac- 
tion upon  milk  casein.  Different  brands  of  rennet-ex- 
tract vary  somewhat  in  their  strength,  that  is,  the 
rapidity  and  completeness  with  which  they  coagulate 
milk  when  used  in  the  same  amount.  It  is  therefore 
important  to  have  a  means  of  testing  their  strength, 
in  order  that  their  value  may  be  definitely  known  and 
that  cheese-makers  may  be  able  to  know  in  advance 
of  using  how  much  they  must  use  for  the  best  results. 
The  Monrad  and  Marschall  tests  are  available  for 
this  purpose. 

In  order  to  test  the  comparative  strength  of  differ- 
ent rennet-extracts,  one  treats  different  portions  of 
the  same  milk  with  the  different  extracts  to  be  tested. 
In  all  other  respects,  the  details  of  the  methods  pre- 
viously given  are  followed.  All  conditions  must  be 
kept  alike  in  the  different  tests.  The  strength  of  the 
rennet-extracts  is  shown  by  the  rapidity  with  which 
the  milk  is  coagulated;  the  stronger  the  rennet,  the 
less  the  time  of  coagulation. 

METHOD  OF  TESTING  PEPSIN 

Pepsin  is  beginning  to  be  used  in  cheese-making  as 
a  substitute  for  rennet-extract.  Vivian  has  worked 
out  the  important  details.  The  scale-pepsin,  of  strength 


126  MODERN    METHODS   OF   TESTING   MILK 

known  as  1-3,000,  prepared  from  stomachs  of  sheep, 
is  recommended.  -It  may  be  used  at  the  rate  of  5 
grams  for  1,000  pounds  of  milk.  In  testing  scale- 
pepsin  by  the  rennet  test,  one  can  dissolve  the  scale- 
pepsin  at  the  rate  of  5  grams  in  4  ounces  of  water  and 
use  this  solution  exactly  like  a  rennet-extract  with 
milk.  It  should  be  tested  in  comparison  with  a  sam- 
ple of  rennet-extract  whose  use  in  cheese-making  has 
been  tested,  the  test  being  made  on  different  portions 
of  the  same  milk. 

TESTING  THE  AGE  OF  MILK  BY  RENNET-TEST 

The  age  of  milks  and  the  care  with  which  they  have 
been  kept  can  also  be  tested  in  a  comparative  way  by 
the  rennet-test,  since  with  the  same  rennet-extract  or 
pepsin  solution  different  milks  generally  coagulate 
more  rapidly  in  proportion  to  the  amount  of  acid  con- 
tained in  them,  especially  if  the  amount  of  lactic  acid 
is  considerable. 


CHAPTER   X 

Methods  of  Testing  Specific  Gravity  and  Solids 
of  Milk  by  the  Lactometer 

The  specific  gravity  of  milk  may  furnish  important 
information,  which  becomes  of  special  value  when 
taken  in  connection  with  the  amount  of  fat  present. 
Thus,  with  the  data  furnished  by  the  specific  gravity 
and  the  per  cent,  of  fat,  we  can  easily  calculate  the 
amount  of  solids  in  milk  and  the  amount  of  solids- 
not-fat. 

THE  SPECIFIC  GRAVITY  OF  MILK 

Definition  of  specific  gravity. — By  the  specific  grav- 
ity of  milk,  we  mean  the  weight  of  a  given  bulk  or 
volume  of  milk  as  compared  with  the  weight  of  an 
equal  volume  of  water  at  the  same  temperature.  To 
illustrate,  suppose  we  have  a  vat  which,  when  just  full 
of  water,  contains  exactly  1,000  pounds  of  water  at 
60°  F.  Now,  if  we  fill  such  a  vat  full  of  milk  of  aver- 
age composition  at  the  same  temperature,  this  amount 
of  milk  weighs  1,032  pounds.  This  is  so  because  the 
milk  contains,  in  addition  to  the  water  in  it,  several 
solid  substances  heavier  than  water.  In  this  illustra- 
tion we  express  the  relation  or  ratio  of  the  equal  vol- 
umes of  water  and  milk  by  dividing  1,032  by  1,000; 
the  result,  1.032,  is  the  specific  gravity  of  the  milk. 

127 


128  MODERN    METHODS   OF   TESTING    MILK 

Variation  in  specific  gravity  of  milk. — Since  the 
specific  gravity  of  milk  largely  depends  upon  the 
amount  of  solids  in  it  heavier  than  water,  the  specific 
gravity  should  vary,  since  we  know  that  the  amount 
of  solids  in  milk  varies  considerably.  And  so  we  find 
the  specific  gravity  of  some  milks  below  1.030  and  of 
some  others  above  1.035  5  DU^  most  normal  milks  from 
herds  of  cows  have  specific  gravities  lying  between 
1.030  and  1.034. 

The  solids  of  milk  heavier  than  water  are  casein, 
albumin  and  milk-sugar.  They  constitute  the  solids- 
not-fat  of  milk  and  have  a  specific  gravity  of  about 
1.500. 

Effect  of  milk-fat  on  specific  gravity  of  milk. — 
Milk-fat  is  lighter  than  water,  its  specific  gravity  be- 
ing about  0.900  compared  with  that  of  water  as  i.ooo. 
Therefore,  an  increase  of  fat  in  milk,  relative  to  the 
other  solids,  lowers  the  specific  gravity  of  milk.  Thus, 
by  adding  cream  to  normal  milk,  we  can  r~ike  its 
specific  gravity  lower  than  that  of  normal  milk.  On 
the  other  hand,  by  removing  fat  from  milk,  we  in- 
crease the  specific  gravity,  because  we  remove  what 
is  lighter,  and  leave  what  is  heavier,  than  water. 

Effect  of  adding  water  and  other  substances  to 
milk. — Water  being  lighter  than  milk,  the  specific 
gravity  of  milk  is  lowered  by  addition  of  water.  There- 
fore, it  is  easily  possible  by  removing  cream  from  nor- 
mal milk  to  increase  the  specific  gravity  and  then,  by 
adding  water,  to  decrease  the  specific  gravity  again 
to  that  of  normal  milk.  The  addition  of  sugar,  salt  or 
any  similar  substance  to  milk  increases  the  specific 
gravity.  Since  water  has  been  the  most  common  adul- 


TESTING   BY    THE   LACTOMETER  129 

terant  of  milk,  it  was  formerly  thought  that  such 
adulteration  could  readily  be  detected  by  ascertaining 
the  specific  gravity ;  but  the  results  of  using  the  spe- 
cific gravity  may  be  very  misleading,  when  consid- 
ered without  reference  to  any  other  factor. 

INFLUENCE   OF   TEMPERATURE  ON    SPECIFIC 
GRAVITY 

Most  liquids  expand  when  heated  and  contract  when 
cooled.  A  vessel  full  of  milk  or  water  at  40°  F.  will 
overflow  when  heated  considerably  higher,  that  is, 
will  hold  less  of  the  fluid,  and  so  the  same  volume 
weighs  less  at  higher  than  at  lower  temperatures. 
From  this  it  is  readily  seen  that  the  specific  gravity  of 
a  liquid  like  water  or  milk  grows  less  when  its  tem- 
perature increases.  On  the  other  hand,  a  vessel  full 
of  water  at  200°  F.  is  not  full  when  cooled  to  40°  F. 
The  same  weight  of  water  occupies  less  volume  and 
its  specific  gravity  is  higher.  Decrease  of  tempera- 
ture increases  the  specific  gravity  of  liquids.  It  is 
therefore  necessary  in  measuring  the  specific  gravities 
of  different  liquids  to  have  the  measurements  made  at 
the  same  temperature,  if  they  are  to  be  comparable. 
The  temperature  commonly  used  is  60°  F. 

METHOD  OF  TESTING  THE  SPECIFIC  GRAVITY 
OF  LIQUIDS 

The  specific  gravity  of  liquids  is  readily  measured 
by  an  instrument  known  as  a  hydrometer.  The  use 
of  such  an  instrument  is  based  on  the  fact  that,  when 
a  solid  body  floats  in  a  liquid,  it  displaces  an  amount 
of  liquid  equal  in  weight  to  the  weight  of  the  floating 


I3O  MODERN    METHODS   OF    TESTING    MILK 

body.  Thus  it  sinks  deeper  in  a  light  liquid  than  in 
a  heavy  one,  because  it  takes  a  larger  volume  of  the 
light  liquid  to  equal  the  weight  of  the  floating  body. 
Such  an  instrument  is  graduated  as  the  re- 
sult of  extensive  experiments,  so  that  the 
specific  gravity  of  the  liquid  in  which  the 
hydrometer  is  placed  can  be  read  at  the 
point  where  the  scale  is  even  with  the  upper 
surface  of  the  liquid.  A  hydrometer  is  cor- 
rect only  for  the  temperature  used  in  stand- 
ardizing it.  When  a  hydrometer  has  a 
scale  specially  adapted  to  the  limits  of  the 
specific  gravity  of  milk,  it  is  called  a  lactom- 
eter. Of  the  various  lactometers  made,  only 
two  are  sufficiently  used  to  deserve  atten- 
tion: (i)  The  Quevenne,  and  (2)  the  New 
York  Board  of  Health,  lactometers. 


THE  QUEVENNE  LACTOMETER 

i 

Description. — This  instrument  (Fig.  48) 

is  a  hydrometer  the  scale  of  which  is  di- 

fyided  into  25  equal  parts,  going  from   15 
to  40.    Each  division  is  called  a  degree,  and 
FIG.  48     every  fifth  degree  is  numbered  on  the  scale. 
LACTOMETER  The   Pomt  marked    15   corresponds   to  the 
point  marked  specific  gravity   1.015  on  an 
ordinary  hydrometer,  and  is  the  point  to  which  it  will 
sink  when  placed  in  liquids  whose  specific  gravity  is 
1.015.    The  40  degree  mark  on  the  Quevenne  lactom- 
eter corresponds   to  the   specific  gravity    1.040  mark 
on  a  hydrometer.    The  relation  between  specific  grav- 


TESTING   BY   THE   LACTOMETER  13! 

ity  and  the  scale  of  the  Quevenne  lactometer  is  shown 
as  follows: 

SPECIFIC  Reading  of 

GRAVITY  Quevenne  lactometer 

1-015 15 

1.020 2O 

1.025 ; 25 

1.030 30 

1.035,  etc.      .     , 35,  etc 

Corrections  for  temperature. — The  Quevenne  lac- 
tometer is  graduated  to  give  correct  results  at  60°  F. 
When  it  is  used  in  milk,  the  milk  should  be  at  60°  F., 
or,  if  at  some  temperature  above  or  below  60°  F.,  a 
correction  of  the  lactometer  reading  must  be  made. 
This  correction  can  be  closely  made  by  adding  to  the 
lactometer  reading  .1  for  each  degree  above  60°  F., 
or  by  subtracting  .1  for  each  degree  below  60°  F. 
For  more  exact  corrections,  consult  table  on  the  fol- 
lowing page. 

The  Quevenne  lactometer  should  carry  a  thermom- 
eter, the  scale  of  which  is  placed  for  convenience  above 
the  lactometer  scale. 

Process  of  using  Quevenne  lactometer. — The  sam- 
ple of  milk  to  be  tested  for  specific  gravity  is  brought 
to  a  temperature  between  50°  and  70°  F.  For  con- 
venience the  milk  is  placed  in  a  cylinder  (Fig.  49), 
which  is  nearly  filled.  The  lactometer  is  carefully 
lowered  into  the  milk  until  it  floats  and  is  allowed  to 
remain  half  a  minute  or  more.  Then  one  reads  and 
records  (i)  the  point  at  which  the  lactometer  scale 
comes  in  contact  with  the  upp'er  surface  of  the  milk; 
and  (2)  the  temperature.  The  lactometer  reading  is- 


132 


8    &   8   8 


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fa 

fa  •«x-o»o»o»o»o»o»oso»o» 

IL 

fa  >»  k-       00       00       00       00       00       00       00       I-       1>       t-       I- 

k 

fa 

fa  •«  ^-.     eo     o      co 

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h 


TESTING   BY   THE   LACTOMETER  133 

then  corrected,  if  the  temperature  is  above  or  below 
60°  F.  For  example,  the  lactometer  settles  in  milk, 
which  is  at  a  temperature  of  65°  F.,  to  the  point 
marked  29.  Adding  to  the  reading  for  correction  .1 
for  each  degree  above  60°  F.,  which  in  this  case  is  .5, 
the  reading  becomes  29.5.  This  means  that  the  spe- 
cific gravity  is  1.0295.  If  the  temperature  of  the 
milk  were  55°  F.,  the  correction  is  subtracted  and 
the  reading  becomes  28.5,  equal  to  specific  gravity 
1.0285. 

THE  NEW  YORK  BOARD  OF  HEALTH 
LACTOMETER 

Description. — This  lactometer  has  been  in  common 
use  among  milk-inspectors  in  the  east- 
ern and  middle  states.     Its  scale  is  quite 
different  from  that  of  the  Quevenne  lac- 
tometer, since  it  is  divided  into  120  equal 
parts.     Beginning  at  the  top  of  the  in- 
strument, the  zero  point  on  the  scale  is 
the  point  to  which  the  lactometer  sinks 
in  water;  and  the  point  is  marked  100 
to  which  it  settles  in  milk  of  specific  grav- 
ity 1,029  at  60°  F.   (Quevenne  reading, 
29),  the  lowest  limit  supposed  to  belong 
to  normal  milk.     The  distance  between 
the  zero  and  100  points  is  divided  into 
100  equal  parts  and  the  scale  is  then  pro- 
longed beyond  the  100  mark  for  20  di-       FIG.  49 
visions  to  120.     The  instrument  is  used  CYLINDER  FOR 
in  the  same  way  as  the  Quevenne  lactom-    LACTOMETER 
eter  in  testing  milk. 


134 


MODERN    METHODS   OF   TESTING    MILK 


1.000 

0 

10- 

1.00V 

50- 

t.010- 

:* 

vote, 

to- 
co 

.» 

1.020- 

/o- 

20' 

JO- 

1.025 

9V 

CO' 

1.030 

no 

»ft 

1.035 

"•• 

3J- 

40 

' 

s 

i 

0 

L 

Comparison  o  f 
the  two  lactometer 
scales. — In  compar- 
ing the  scales  of  the 
Quevenne  and  Board 
of  Health  lactom- 
eters, the  following 
points  will  make  clear 
their  relations:  (r) 
The  zero  point  on 
both  instruments  in- 
dicates the  specific 
gravity  of  water, 
that  is,  i. ooo.  (2) 
On  the  B.  of  H.  lac- 
tometer, the  100  di- 
visions or  degrees 
from  o  to  100  corre- 
spond to  29  divisions 
on  the  Quevenne. 
Therefore  one  de- 
gree on  the  B.  of  H. 
lactometer  c  o  r  r  e- 
sponds  to  .29  degree 
on  the  Quevenne.  To 
convert  the  B.  of  H. 
lactometer  reading 
into  that  of  the 
Quevenne,  multiply 
the  reading  of  the 
former  by  .29.  The 
relation  of  the  specific  gravity  scale  of  a  hydrometer 


FIG.  50 — COMPARISON  OF  DIFFERENT 

SPECIFIC  GRAVITY    SCALES 
S  is  specific  gravity  scale;  Nis  New  York 
Board  of  Health  lactometer;  Q  is 


UNIVERSITY 

OF 


TESTING 


ACTOMETER 


135 


to  the  scales  of  the  Quevenne  and  B.  of  H.  lactometer 
is  shown  in  Fig.  50. 


TABLE  II. — DEGREES  ON  QUEVENNE  LACTOMETER  CORRESPONDING  TO 
DEGREES  ON   NEW  YORK  BOARD  OF  HEALTH  LACTOMETER 


BOARD  OF 
HEALTH 

QUEVENNE 

BOARD  OF 
HEALTH 

QUEVENNE 

BOARD  OF 
HEALTH 

QUEVENNE 

Degrees 

Degrees 

Degrees 

Degrees 

Degrees 

Degrees 

60 

17.4 

81 

23.5 

101 

29.3 

61 

17.7 

82 

23.8 

102 

29.6 

62 

18.0 

83 

24.1 

103 

29.9 

63 

18.3 

84 

24.4 

104 

30.2 

64 

18.6 

85 

24.6 

105 

30.5 

65 

18.8 

86 

24.9 

106 

30.7 

66 

18.1 

87 

25.2 

107 

31.0 

67 

19.4 

88 

25.5 

108 

31.3 

68 

19.7 

89 

25.8 

109 

31.6 

69 

20.0 

90 

26.1 

110 

31.9 

70 

20.3 

91 

26.4 

111 

32.2 

71 

20.6 

92 

26.7 

112 

32.5 

72 

20.9 

93 

27.0 

113 

32.8 

73 

21.2 

94 

27.3 

114 

33.1 

74 

21.5 

95 

27.6 

115 

33.4 

75 

21.7 

96 

27.8 

116 

33.6 

76 

22.0 

97 

28.1 

117 

33.9 

77 

22.3 

98 

28.4 

118 

34.2 

78 

22.6 

99 

28.7 

119 

34.5 

79 

22.9 

100 

29.0 

120 

34.8 

80 

23.2 

.... 

,... 

.... 

136  MODERN    METHODS   OF   TESTING    MILK 

Corrections  for  temperature. — In  using  the  B.  of 
H.  lactometer,  correction  is  made  for  temperatures 
above  or  below  60°  F.  For  each  degree  of  tempera- 
ture of  milk  above  60°  F.,  add  .3  to  the  lactometer 
reading,  and  for  each  degree  below  60°  F.  subtract  .3 
from  the  reading. 

PRECAUTIONS  IN  TESTING  SPECIFIC  GRAVITY 
OF  MILK 

1.  Milk  should,  for  best  results,  not  be  examined 
until   i  to  2  hours  or  more  after  milking,  since  the 
specific  gravity  of  milk  is  lower  for  a  while  after  be- 
ing drawn  than  it  is  later,  due  chiefly  to  the  presence 
of  gases. 

2.  The  sample  of  milk  must  be  completely  mixed. 

3.  The  lactometer  must  be  kept  clean. 

4.  In  milk  which  has  been  preserved  by  potassium 
bichromate,  the  specific  gravity  is  about  one  degree 
higher   than   in  the   normal   milk,   in   case   the   usual 
amount  of  bichromate  has  been  added.   (See  p.  30). 

VALUE  OF  LACTOMETER  IN  DETECTING  ADUL- 
TERATED MILK 

The  value  of  the  lactometer  in  detecting  adulterated, 
especially  watered,  milk  was  formerly  overestimated. 
Taken  alone,  the  results  given  by  the  lactometer  may 
be  thoroughly  unreliable  and  misleading.  It  has 
come  to  be  quite  generally  recognized  that  the  proper 
use  of  the  lactometer  in  milk  inspection  is  largely  to 
indicate  whether  a  sample  is  suspicious  and  to  furnish 
a  guide  as  to  whether  it  is  necessary  to  take  a  sam- 
ple for  further  detailed  investigation  by  chemical  anal- 


TESTING   BY   THE   LACTOMETER  137 

ysis.  As  already  stated,  a  milk  which  is  both  skimmed 
and  watered  may  appear  to  be  entirely  normal  by  the 
lactometer. 

METHOD    OF   TESTING   MILK   FOR   SOLIDS   BY 
LACTOMETER 

As  the  result  of  extended  studies  of  the  relations  ex- 
isting between  the  specific  gravity  of  milk,  milk-fat 
and  milk-solids,  rules  have  been  formulated  by  means 
of  which  it  is  possible  to  calculate  with  a  close  degree 
of  approximation  the  total  solids  of  milk,  when  one 
knows  the  percentage  of  fat  and  the  (Quevenne)  lac- 
tometer reading. 

Babcock's  formulas  for  solids  and  solids-not-fat.— 
The  following  formulas  were  devised  by  Dr.  Bab- 
cock: 

(1)  Formula  for  determining  solids-not-fat,  —  Sol- 
ids-not-fat=^L+.2f,   in   which   L   is   the   reading  of 
the  Quevenne  lactometer  and  f  is  the  per  cent,  of  fat 
in  the  milk. 

(2)  Formula  for  determining  solids  in  milk.  —  Total 


These  formulas  can  be  expressed  in  the  form  of 
rules  as  follows  : 

Rule  i.  —  To  find  the  per  cent,  of  solids-not-fat  in 
milk,  divide  the  reading  of  the  Quevenne  lactometer 
by  4,  and  to  the  result  add  the  per  cent,  of  fat  in  the 
milk  multiplied  by  .2. 

Rule  2.  —  To  find  the  per  cent,  of  solids  in  milk,  di- 
vide the  Quevenne  lactometer  reading  by  4,  and  to 
the  result  add  the  per  cent,  of  fat  multiplied  by  1.2. 

Examples:  —  A  milk  containing  4  per  cent,  of  fat 


138 


MODERN    METHODS   OF   TESTING   MILK 


I 


shows  a  lactometer  reading  of  32.  What 
is  the  per  cent,  (a)  of  solids-not-fat,  (b) 
of  total  solids? 

(a)  The  lactometer  reading  (32),  di- 
vided by  4,  equals  8.  The  per  cent,  of 
fat  (4),  multiplied  by  .2,  equals  .8.  Add- 
ing 8  and  .8,  we  obtain  8.8  as  the  per 
cent,  of  solids-not-fat. 

b)  The  per  cent,  of  total  solids  in  the 
milk  is  12.8  per  cent.;  for  the  lactometer 
reading,  divided  by  4,  equals  8,  the  per 
cent,  of  fat  (4)  multiplied  by  1.2  equals 
4.8,  and  Spins  4.8  equals  12.8. 

Richmond's  slide-rule  for  calculating 
solids. — Instead  of  going  through  the 
details  of  calculation  to  estimate  solids 
in  milk,  Richmond  uses  a  slide-rule  which 
is  a  clever  mechanical  calculating  device. 
(Fig.  51).  The  results  obtained  in  this 
manner  agree  closely  with  those  given  by 
Babcock's  formulas.  The  method  of 
using  the  slide-rule  is  as  follows :  De- 
termine (i)  the  Ouevenne  lactometer 
reading,  (2)  the  temperature  of  the 
milk,  and  (3)  the  per  cent,  of  fat  in  the 
milk.  Then  set  the  central  slide  of  the 
rule  so  that  the  observed  lactometer  read- 
ing is  opposite  the  60  degree  (tempera- 
ture) mark.  The  true  lactometer  read- 
ing is  found  opposite  the  line  indicating 
the  observed  temperature  of  the  milk.  Having  thus 
corrected  the  lactometer  reading  for  temperatures 


FIG.  51 
RICHMOND'S 
SLIDE-RULE 


TESTING  BY  THE   LACTOMETER  139 

other  than  60°  R,  next  set  the  arrow  on  the  sliding 
portion  of  the  rule  opposite  the  per  cent,  of  fat  found 
in  the  milk  and  read  the  total  solids  contained  in  the 
milk  corresponding  with  the  corrected  lactometer  read- 
ing or  specific  gravity. 

To  illustrate,  suppose  the  lactometer  reading  of  a 
sample  of  milk  at  70°  F.  is  30  and  the  per  cent,  of  fat 
is  4.  To  correct  for  temperature  and  find  what  the 
lactometer  reading  would  be  at  60°  F.,  the  lactometer 
reading  (30)  is  placed  opposite  the  little  arrow  at  60 
on  the  temperature  scale.  Then,  looking  at  the  point 
of  temperature  70,  we  find  opposite  this  point  31.3, 
which  is  the  corrected  or  true  reading.  Next,  we 
place  the  arrow  opposite  the  4  per  cent,  mark,  as  the 
milk  contains  4  per  cent,  of  fat,  and  then  notice  where 
the  point  31.3  (specific  gravity),  comes  in  contact  with 
the  solids  scale.  It  corresponds  closely  to  12.8,  which 
is  the  per  cent,  of  total  solids  in  the  sample  of  milk 
examined.  Some  practice  with  this  slide-rule  enables 
one  to  work  rapidly. 

Specific  gravity  of  milk-solids. — The  following  rule 
has  been  proposed  by  Fleischmann  for  calculating  the 
specific  gravity  of  milk-solids:  Multiply  the  specific 
gravity  of  the  milk  by  100,  from  the  result  subtract 
100  and  divide  this  result  by  the  specific  gravity  of 
the  milk.  Subtract  the  last  result  from  the  per  cent, 
of  total  solids  in  the  milk  and  then  divide  by  this  re- 
sult the  per  cent  of  total  solids  of  the  milk.  This  may 
also  be  expressed  by  the  following  formula: 


Sp.  gr.  milk-solids= 


milk-solids 


milk-solids — (rooXsp.  gr.) — 100 
sp.  gr. 


I4O  MODERN    METHODS   OF   TESTING    MILK 

Example:  A  sample  of  milk  contains  12.5  per  cent. 
of  solids  and  has  a  specific  gravity  of  1.031; 
—  what  is  the  specific  gravity  of  the  milk-solids? 


This  calculation  may  assist  in  determining  whether 
a  sample  of  suspected  milk  has  been  adulterated.  The 
variations  of  the  specific  gravity  of  milk-solids  is  slight, 
ranging  between  1.25  and  1.34.  Milks  richer  in  fat 
have  solids  of  lower  specific  gravity.  The  specific 
gravity  of  milk-solids  is  not  changed  by  watering  milk, 
but  is  increased  by  removing  fat  or  by  addition  of 
skimmed  milk.  Hence,  milk  whose  solids  have  a 
specific  gravity  above  1.34  is  suspected  of  being 
skimmed,  while  a  specific  gravity  above  1.40  is  re- 
garded as  clear  evidence  of  skimming. 


CHAPTER   XI 

Methods  of  Testing  Milk  and  Milk  Products 
for  Adulterations 

Milk  is  commonly  adulterated  in  one  of  the  follow- 
ing ways:  (i)  By  addition  of  water,  (2)  by  removal 
of  fat  (skimming)  or  addition  of  skim-milk,  (3)  by 
addition  of  substances  not  normally  found  in  milk, 
such  as  preservatives  and  coloring  matter.  All  these 
forms  of  adulteration  may  occur  in  the  same  milk. 

DETECTION   OF  ADDED   WATER   IN   MILK 

Since  water  in  milk  is  the  same  chemical  compound 
as  the  water  found  everywhere  else,  it  is  impossible 
to  identify  added  water  in  milk  by  any  direct  test  for 
special  properties.  The  presence  of  added  water  in 
milk  can  be  learned  with  certainty  only  by  indirect 
means  and  even  then  not  with  certainty  in  all  sus- 
pected cases.  An  examination  of  milk  direct  from 
the  cow  or  herd,  when  this  is  possible,  may  settle  the 
question  of  watering.  The  lactometer,  while  unrelia- 
ble as  a  sure  means  of  detecting  added  water  in  milk, 
may  give  a  helpful  suggestion,  used  as  a  preliminary 
test.  Thus,  if  a  milk  shows  a  specific  gravity  under 
1.028,  it  is  open  to  the  suspicion  of  being  watered,  and 
should  then  be  carefully  examined  in  other  ways. 

Most  states  fix  legal  standards  for  the  per  cent,  of 
water,  solids,  fat,  and  solids-not-fat  in  milk,  and  any 

141 


142  MODERN    METHODS   OF    TESTING    MILK 

milk  falling  below  the  fixed  limit  in  composition  is 
regarded  as  adulterated.  'Thus,  a  standard  common 
to  several  states  is  12  per  cent,  of  solids  and  3  per  cent, 
of  fat.  This  means  also  that  such  legal-standard  milk 
must  not  contain  more  than  88  per  cent,  of  water  or 
less  than  9  per  cent,  of  solids-not-fat. 

The  relations  of  the  different  constituents  of  milk 
have  been  studied  and  formulas  have  been  devised 
which  enable  one  in  an  approximate  way  to  tell  how 
much  water  has  been  added  to  a  sample  of  milk  be- 
yond the  amount  allowed  by  the  standards.  These 
formulas  are  based  on  the  assumption  that  the  limits 
fixed  by  the  legal  standard  represent  the  lowest 
amounts  of  solids  and  fat  found  in  normal  milk,  and 
they  are  correct  only  when  the  original  milk  contains 
the  lowest  percentages  given  in  the  legal  standard. 

In  calculating  the  amount  of  added  water  in  milk, 
the  amount  of  solids-not-fat  (total  solids  minus  fat) 
is  used  as  a  basis.  The  procedure  is  as  follows: 

(1)  Determine  the  per  cent,  of  fat  in  the  suspected 
sample. 

(2)  Take  the  lactometer  (Quevenne)   test. 

(3)  Determine   the   amount   of    solids-not-fat   ac- 
cording to  the  formula,  %L+.2f.  (p.  137). 

(4)  Apply  the  following  rule:  Multiply  the  per  cent, 
of  solids-not-fat  by  100  and  divide  the  result  by  the 
legal   standard   for  solids-not-fat.     Subtract  the   last 
result  from  100  and  the  result  is  the  per  cent,  of  ad- 
ded water  in  the  sample  of  suspected  milk.     This  rule 
is  expressed  in  the  form  of  the  following  formula: 

per  cent,  of  solids-not-fat  X  100. 
Per  cent,  of  added  water^ioo-^^-^^  fof  solids.not.fat> 


TESTING   MILK  FOR  ADULTERATIONS  143 

This  formula  gives  only  the  amount  of  water 
added  beyond  the  limit  fixed  by  the  legal  standard 
and  is  correct  only  if  the  original  milk  contained  the 
amount  of  solids-not-fat  prescribed  by  the  standard 
(usually  9  per  cent.).  Hence,  in  cases  of  watered 
milk,  the  calculated  amount  of  water  added  is  gener- 
ally less  than  the  real  amount  added. 

Example  :  A  milk  is  found  to  contain  3  per  cent,  of 
fat  and  to  show  a  lactometer  reading  of  27.  Applying 
the  formula  for  finding  the  amount  of  solids-not-fat, 
the  per  cent,  is  7.35.  If  the  legal  standard  for  solids- 
not-fat  is  9,  then  the  formula  becomes 


the  per  cent,  of  added  water  that  is  contained  in  the 
milk,  assuming  that  it  contained  9  per  cent,  of  solids- 
not-fat  before  being  watered. 

The  following  rule  can  also  be  used:  Add  together 
the  lactometer  reading  and  the  per  cent,  of  fat  present 
in  the  milk,  divide  the  sum  by  36,  multiply  the  result 
by  loo  and  subtract  the  last  result  from  100.  Ex- 
pressed as  a  formula,  this  becomes 

Per  cent,  of  |  •         ...  lactometer  reading  +  per  centof  fatv^ 

added  water  \  m  ™ilk=ioo—  36  ~X  IO°. 

An  examination  of  the  serum  of  milk  by  means  of 
a  refractometer  gives,  probably,  the  most  reliable 
means  of  detecting  added  water  in  milk,  but  this 
method  is  available  only  for  special  workers.  For  its 
details  see  "Food  Inspection  and  Analysis,"  by  Leach, 
(P-  139). 


144  MODERN    METHODS   OF    TESTING    MILK 

DETECTION  OF  SKIMMED   MILK 

The  percentage  of  fat  in  milk  in  relation  to  the 
other  milk-solids  is  reduced  either  (i)  by  direct  re- 
moval of  fat  through  some  process  of  .skimming  or 
(2)  by  the  addition  of  separator  skim-milk  to  nor- 
mal milk.  Milk  containing  less  than  3  per  cent,  of 
fat  is  generally  skimmed.  Watering  milk  does  not 
disturb  the  relations  of  the  constituents  of  milk  to 
one  another,  since  it  reduces  the  percentages  of  all 
uniformly,  but  the  removal  of  fat  does  very  seriously 
affect  the  amounts  of  the  constituents  in  respect  to 
their  relative  percentages.  In  skimming  milk,  the 
solid  constituent  most  largely  removed  is  fat,  com- 
paratively little  casein,  sugar,  etc.,  being  taken  with 
the  fat.  The  removal  of  fat  therefore  leaves  the  milk 
containing  less  fat  but  with  most  of  its  casein,  sugar, 
etc.,  still  remaining.  In  normal  herd  milk,  containing 
over  3  per  cent,  of  fat,  the  percentage  of  fat  is  rarely 
as  low  as  the  percentage  of  casein  and  albumin.  In 
5,500  analyses  of  samples  of  American  milks,  compiled 
by  the  author,  with  a  fat  content  lying  between  3  and 
5  per  cent.,  the  fat  averages  3.92  per  cent.,  and  the  ca- 
sein and  albumin  together,  3.20  per  cent. ;  that  is,  for  I 
part  of  casein  and  albumin  there  is*an  average  of 
1.225  parts  of  fat.  In  skimming  such  milk,  the  fat  may 
be  decreased  to  I  per  cent,  or  .1  per  cent.,  but  the  re- 
maining milk  still  contains  about  3.20  per  cent,  of 
casein  and  albumin.  Milk  is  open  to  the  suspicion  of 
being  skimmed,  when  the  percentage  of  fat  falls  be- 
low that  of  the  casein  and  albumin. 

The  percentage  of  fat  removed,  based  on  the  legal 


TESTING   MILK  FOR  ADULTERATIONS  145 

standard,  may  be  calculated  by  the  following  rule : 
Multiply  the  per  cent,  of  fat  in  the  milk  by  100,  di- 
vide the  result  by  the  legal  standard  for  fat  and  sub- 
tract this  from  100;  or  expressed  as  a  formula: 

The  per  cent,  of  fat  removed=ioo—  ?_><_«£  This 
formula  is  true  only  for  milks  originally  containing  3 
per  cent,  of  fat  and  so  its  results  are  generally  much 
below  the  truth.  For  example,  in  a  milk  containing 
originally  5  per  cent,  of  fat,  which  has  been  skimmed 
to  2.50  per  cent.,  thus  removing  50  per  cent,  of  the 
fat  in  the  milk,  the  above  formula  would  indicate  that 
only  1 6.6  per  cent,  of  the  fat  had  been  removed.  In 
most  cases  results  nearer  the  actual  truth  are  given 
by  substituting  3.75  for  3  in  the  formula. 


GENERAL  METHOD  FOR  JUDGING  WATERED 
AND  SKIMMED  MILK 

Having  found  in  a  sample  of  milk  ( I )  the  per  cent, 
of  fat,  (2)  the  specific  gravity  of  the  milk  and  (3)  of 
the  milk-solids,  (4)  the  per  cent,  of  solids,  and  (5)  of 
solids-not-fat,  one  may  arrive  at  fairly  safe  conclu- 
sions in  regard  to  the  watering  and  skimming  by 
making  comparison  with  the  percentages  of  constitu- 
ents present  in  average  normal  milk.  In  forming  such 
conclusions,  the  following  facts  should  be  kept  in 
mind: 

1.  Water  has  a  lower  specific  gravity  than  milk. 

2.  Watering  milk  decreases  (a)  the  lactometer  read- 
ing, (b)  the  fat,  (c)  total  solids,  and  (d)  solids-not-fat. 

3.  Water  has  a  higher  specific  gravity  than  milk-fat. 


146  MODERN    METHODS   OF   TESTING    MILK 

4.  Skimming  milk  (a)  increases  the  lactometer  read- 
ing, (b)  decreases  the  fat  and  total  solids,  (c)  slightly 
increases  the  solids-not-fat,  and  (d)  increases  the  spe- 
cific gravity  of  the  milk-solids. 

5.  Skimming  and  watering  decrease  all  constituents, 
but  lower  the  fat  more  in  proportion  than  the  solids 
and  solids-not-fat. 

6.  Skimming  and  watering  may  produce  the  same 
specific  gravity  as  in  normal  milk. 

7.  The  amount  of  fat  in  milk  is  more  variable  than 
the  amount  of  solids-not-fat. 

8.  Herd   milk   which   shows   a   lactometer   reading 
above  33.5,  along  with  a  low  percentage  of  fat,  and  a 
specific  gravity  of  solids  above  1.40,  can  be  regarded 
as  skimmed. 

9.  Herd  milk  showing  a  lactometer  reading  below 
28  may  be  regarded  as  watered,  especially  with  low 
fat,  solids  and  solids-not-fat. 

Milk  is  watered  when  (i)  the  specific  gravity  of 
the  milk  is  low,  (2)  the  percentage  of  fat  and  solids- 
not-fat  is  low  and  (3)  the  specific  gravity  of  the  milk- 
solids  is  between  1.25  and  1.35. 

Milk  is  skimmed  when  (i)  the  specific  gravity  of 
the  milk  and  of  the  milk-solids  is  high;  when  (2) 
the  per  cent,  of  solids-not-fat  is  high,  and  when  (3) 
the  per  cent,  of  fat  and  solids  is  low. 

Milk  is  watered  and  skimmed  when  (i)  the  spe- 
cific gravity  of  the  milk  is  normal  or  otherwise,  (2) 
the  specific  gravity  of  the  milk-solids  is  normal  or  high, 
and  (3)  the  per  cent,  of  fat  and  solids-not-fat  is  low, 


TESTING  MILK  FOR  ADULTERATIONS  147 

DETECTION  OF  FOREIGN  SUBSTANCES  IN  MILK 

The  foreign  substances  most  frequently  found  in 
milk  are  preservatives  and  coloring  matters.  The  pre- 
servatives in  common  use  are  formalin,  boric  acid, 
borax  and  sodium  bicarbonate.  The  coloring  matters 
generally  used  are  annatto  and  coal-tar  dyes  (azo- 
colors),  which  are  added  to  milk  to  make  it  look  rich, 
and,  especially  in  case  of  skimmed  and  watered  milk, 
to  cover  up  the  signs  of  such  adulterations. 

Test  for  annatto. — To  10  cc.  of  milk  in  a  test-tube 
add  10  cc.  of  ether,  shake  vigorously  and  let  stand  un- 
til the  ether  separates  on  top  of  the  milk.  If  annatto 
is  present,  the  layer  of  ether  will  be  yellow,  the  depth 
of  color  depending  on  the  amount  of  annatto  present. 

Test  for  Coal-Tar  Dyes. — The  azo-colors,  which 
are  the  ones  most  commonly  used  in  coloring  milk,  may 
be  detected  by  adding  10  cc.  of  milk  to  10  cc.  of  strong 
hydrochloric  acid  and  mixing,  when  a  pink  coloration 
appears. 

Tests  for  Formalin. — Formalin,  which  is  a  40 
per  cent,  solution  of  formaldehyde,  is  commonly  di- 
luted and  sold  under  such  names  as  "Freezine,"  "Ice- 
line,"  etc.,  which  contain  from  2  to  6  per  cent,  of  for- 
maldehyde. In  making  the  Babcock  test  in  milk,  the 
presence  of  formalin  may  be  shown  when  a  marked 
violet  layer  forms  at  the  junction  of  the  acid  and  milk 
just  after  pouring  the  acid  into  the  test-bottle.  The  test 
may  also  be  performed  by  taking  10  cc.  of  milk  in  a 
test-tube  or  Babcock  test-bottle,  and  adding  about  5 
cc.  of  sulphuric  acid,  such  as  is  used  in  the  Babcock 
test,  pouring  the  acid  down  the  side  of  the  tube  so 
that  it  does  not  mix  with  the,  milk. 


148  MODERN    METHODS    OF    TESTING    MILK 

Leach's  test,  which  is  more  delicate,  is  performed 
as  follows:  Make  a  solution  of  hydrochloric  acid  (spe- 
cific gravity  1.2)  containing  2  cc.  of  10  per  cent,  ferric 
chloride  per  liter.  Add  10  cc.  of  this  solution  to  10 
cc.  of  milk  in  a  white  teacup  and  heat  slowly  over  a 
flame  to  boiling,  giving  the  cup  a  rotary  motion.  If 
formalin  is  present,  a  violet  coloration  appears,  vary- 
ing in  depth  with  the  amount  present. 

Test  for  borax  and  boric  acid. — To  25  cc.  of  milk 
add  lime  water,  until  the  milk  is  alkaline,  evaporate  to 
dryness  and  burn  to  an  ash  in  a  small  porcelain  or 
platinum  dish.  To  the  ash  add  a  few  drops  of  dilute 
hydrochloric  acid,  not  too  much;  then  add  a  few  drops 
of  water  and  place  in  this  water  solution  a  strip  of 
turmeric-paper  (obtainable  at  drug-stores).  Then  dry 
the  paper,  when  a  cherry-red  color  will  appear  on  the 
paper  if  either  borax  or  boric  acid  is  present.  This  test 
is  made  still  more  certain  by  moistening  the  reddened 
paper  with  a  drop  of  an  alkali  solution,  when  the  pa- 
per turns  to  a  dark-olive  color  in  the  presence  of  borax 
or  boric  acid. 

Test  for  sodium  carbonate. — To  10  cc.  of  milk  add 
10  cc.  of  alcohol  and  a  few  drops  of  a  I  per  cent,  so- 
lution of  rosolic  acid.  Carbonates  are  present  if  a 
rose-red  color  appears,  while  pure  milk  shows  a  brown- 
ish-yellow color. 

ADULTERATIONS  OF  CREAM 

The  adulterants  of  cream  are  the  same  as  those  for 
milk  and  are  detected  in  the  same  manner.  Gelatine 
and  sucrate  of  lime  are  used  to  some  extent  to  give 
cream  a  greater  consistency. 


TESTING   MILK  FOR  ADULTERATIONS  149 

ADULTERATIONS  OF  BUTTER 

The  most  common  adulteration  of  butter  is  substi- 
tution, in  part  or  in  whole,  of  fat  other  than  butter- 
fat,  such  as  products  from  beef-fat  and  lard.  Occa- 
sionally preservatives  are  found,  such  as  occur  in  milk. 
"Renovated"  or  "process"  butter  is  made  from  refuse 
butter  that  can  not  be  disposed  of  otherwise  on  the 
market.  Excessive  water  or  casein  should  be  regarded 
as  an  adulteration.  Harmless  coloring  matter  has  been 
universally  allowed.  The  absolute  identification  of 
such  adulterants  as  oleomargarin  requires  somewhat 
elaborate  chemical  methods.  Only  simple  tests  can 
be  given  here. 

Foam-test  for  oleomargarin  and  "renovated"  but- 
ter.— Melt  in  an  ordinary  tablespoon  a  piece  of  the 
suspected  butter  about  the  size  of  a  small  chestnut, 
holding  it  over  a  small  flame, — a  candle  flame  will  do. 
Stir  the  fat,  while  melting,  with  a  match  or  similar 
stirrer.  Then  lower  the  spoon  into  the  flame  and  let 
the  fat  boil  vigorously,  stirring  thoroughly  several 
times  during  the  boiling  and  not  neglecting  the  outer 
edges.  Oleomargarin  and  "renovated"  butter  boil 
with  marked  noise,  sputtering  more  or  less  and  pro- 
ducing little  or  no  foam.  Genuine  butter  generally 
boils  with  much  less  noise  and  foams  up  vigorously. 

Milk-Test  for  oleomargarin. — In  a  tin  measuring- 
cup  take  about  one  gill  of  sweet  milk  or  water,  heat 
to  about  140°  F.  and  then  add  a  slightly  rounded  tea- 
spoonful  of  the  suspected  sample.  Stir  with  a  small 
piece  of  wood,  about  the  size  of  a  match  or  smaller, 
until  the  fat  is  melted.  Then  immerse  the  cup  to  about 
one-third  of  its  height  in  a  pan  of  water  in  which  there 


150     ,         MODERN    METHODS   OF    TESTING    MILK 

are  several  large  pieces  of  ice.  Stir  the  liquid  contin- 
uously, alternating  a  circular  and  crosswise  motion, 
until  the  fat  hardens,  when  it  can  be  easily  collected 
into  one  lump  by  means  of  the  wooden  stirrer,  if  it  is 
oleomargarin ;  but,  if  butter,  the  fat  will  form  little 
granules  and  can  not  be  collected  in  one  lump.  When 
milk  is  used  in  the  test,  it  should  contain  as  little  fat 
as  possible.  In  this  test  "renovated"  butter  behaves 
like  genuine  butter. 

ADULTERATIONS  OF  CHEESE 

Only  two  kinds  of  adulteration  are  common  in 
American  cheddar  cheese:  (i)  The  removal  of  fat  in 
varying  degrees  producing  so-called  skim-cheese,  and 
(2)  the  use  of  fat  other  than  milk- fat,  producing  the 
so-called  filled  cheese.  Harmless  coloring  matter  is 
allowed.  Cheese  containing  less  than  32  per  cent,  of 
fat  can  be  regarded  as  having  been  made  from  milk 
containing  less  than  its  normal  amount  of  fat.  The 
per  cent,  of  fat  in  filled  cheese  is  generally  lower  than 
in  cheese  made  from  normal  milk. 


CHAPTER   XII 

The  Babcock  Test  Applied  to  Farm  Conditions 

The  Babcock  test  finds  application  on  the  farm  of 
every  dairyman  in  one  or  more  of  the  following  ways : 

i)  In  testing  the  quality  of  milk  in  respect  to  fat 
produced  by  individual  cows  and  by  the  herd. 

(2)  In  testing  cream. 

(3)  In  testing  skim-milk. 

(4)  In  testing  buttermilk. 

(5)  In  testing  milk  and  cream  as  a  means  of  self- 
protection. 

TESTING  COWS 

The  most  effective  test  of  the  value  of  a  dairy  cow 
is  the  production  of  milk  and  of  milk-fat.  Evidence 
has  been  carefully  collected  showing  that  many  cows 
in  this  country  are  kept  at  an  actual  loss.  The 
owners  of  such  cows  may  be  conscious  of  the  fact 
that  they  are  not  prospering,  but  without  having  any 
idea  of  the  cause.  The  amount  of  fat  in  milk  required 
for  various  purposes  differs  somewhat.  For  ordi- 
nary market  purposes,  where  consumers  take  as  a 
matter  of  course  any  kind  of  milk  delivered  to  them, 
the  most  profitable  cow  is  the  one  producing  a  large 
yield  of  milk,  which  generally  means  a  low  percentage 
of  fat,  frequently  just  enough  to  keep  above  the  legal 
standard.  The  statement  applies  to  milk  sold  by  bulk 


152  MODERN    METHODS   OF   TESTING   MILK 

or  by  weight  alone,  whether  sold  for  direct  consump- 
tion or  taken  to  a  cheese-factory  or  creamery.  But 
whenever  milk  is  paid  for  according  to  its  percentage 
of  fat,  as  in  certain  forms  of  market  milk,  at  cream- 
eries, at  condenseries,  and  at  progressive  cheese-fac- 
tories, the  cow  producing  the  largest  amount  of  milk- 
fat  will  nearly  always  be  found  the  most  profitable. 
As  a  rule,  a  pound  of  milk-fat  can  be  produced  at  less 
cost  in  rich  milk  than  in  poor  milk.  The  only  method 
of  ascertaining  accurately  the  value  of  a  cow  or  of  a 
herd  for  the  production  of  milk-fat  is  by  testing  the 
milk.  The  real  object  of  a  test  is  to  find  the  total  num- 
ber of  pounds  of  fat  produced  in  the  milk  for  a  defin- 
ite period  of  time,  the  most  satisfactory  unit  being  one 
period  of  lactation,  that  is,  from  the  time  of  calving 
to  the  time  of  becoming  dry. 

In  testing  the  value  of  a  cow  for  the  production  of 
milk- fat,  two  factors  must  be  considered:  (i)  The 
amount  of  milk  produced  and  (2)  the  per  cent,  of  fat 
in  the  milk.  The  first  amount  is  obtained  by  weigh- 
ing the  milk,  and  the  second  by  testing  the  milk  by 
the  Babcock  test.  From  these  data  the  amount  of 
milk-fat  produced  is  easily  found. 

In  applying  the  Babcock  test  on  the  farm  to  indi- 
vidual cows,  certain  details  need  to  be  considered, 
such  as  (i)  the  duration  of  the  testing,  (2)  the  fre- 
quency of  testing,  (3)  the  method  of  sampling,  (4) 
weighing  the  milk,  (5)  keeping  records,  and  (6)  cal- 
culating results.  In  carrying  out  the  work  of  the 
milk-test,  all  necessary  details  are  given  in  Chapter 

IV,  p.  53- 

Duration  of  testing. — For  best  results,  the  tests 


FARM    CONDITIONS  153 

should  be  made  at  intervals  for  a  whole  period  of  lac- 
tation. 

Frequency  of  testing. — It  is  not  practicable  to  test 
the  milk  of  every  milking  for  fat  and  it  is  not  neces- 
sary. On  the  other  hand,  the  testing  of  a  single  milk- 
ing or  of  a  day's  milk  or  even  of  a  week's  milk  is  in- 
sufficient, since,  for  many  reasons,  the  percentage  of 
fat  may  vary  greatly  from  one  time  to  another.  The 
following  plan  combines  a  high  degree  of  accuracy 
with  the  least  amount  of  labor:  Make  the  first  fat- 
test in  about  two  weeks  after  the  cow  calves  and  then 
repeat  it  regularly  once  in  two  weeks  during  the  period 
of  lactation.  Even  a  monthly  testing  will,  however, 
give  fairly  accurate  results. 

Method  of  sampling. — When  a  single  cow's  milk 
is  to  be  tested,  the  following  precautions  should  be 
observed  in  taking  the  sample: 

( i )  The  cow  must  be  milked  dry  at  the  milking  pre- 
vious to  the  one  to  be  tested.  (2)  On  the  day  of  milk- 
ing for  the  test,  the  cow  is  milked  as  completely  as 
possible  each  time.  (3)  After  the  morning's  milk- 
ing, the  milk  is  well  mixed  by  pouring  from  one  pail 
to  another  or  by  stirring  with  a  dipper,  and  about  a 
gill  is  at  once  dipped  out  and  poured  into  a  pint  fruit- 
jar,  which  has  been  thoroughly  cleaned  and  scalded. 
The  sample  is  kept  in  a  cool  place.  Repeat  the  samp- 
ling with  the  evening's  milk  or  with  each  milking,  if 
the  cow  is  milked  more  than  twice  a  day,  adding  a  sam- 
ple of  each  to  the  jar  containing  the  morning's  milk. 
(4)  Make  a  test  before  the  milk  can  sour,  mixing  well 
before  taking  samples  for  the  test  by  pouring  back 
and  forth  a  few  times  from  one  vessel  to  another.  If 


154  MODERN    METHODS   OF   TESTING    MILK 

it  is  impossible  to  make  the  test  promptly,  add  bi- 
chromate of  potash  to  preserve  the  sample,  as  directed 
on  p.  30.  (5)  In  testing  the  milk  of  several  cows  at 
the  same  time,  label  each  sample- jar  with  the  number 
or  name  of  the  cow  furnishing  the  milk.  (6)  If  the 
milk  is  to  be  tested  also  for  solids  by  the  lactometer, 
take  about  a  half-pint  sample  from  each  milking. 

More  strictly  accurate  results  are  secured  if  each 
milking  is  sampled  by  a  tube,  as  stated  on  p.  27. 

Weighing  milk. — In  testing  a  cow,  the  milk  must 
always  be  weighed  on  the  testing  day  immediately  af- 
ter the  milking  is  completed.  As  it  is  so  easy  to  weigh 
milk,  it  is  desirable  to  weigh  the  milk  at  every  milking, 
or,  at  least,  on  two  or  three  days  each  week.  Accurate 
spring  scales  of  moderate  cost  are  available. 

Keeping  records. — Records  of  each  cow  tested 
should  be  carefully  kept,  the  following  facts  being  re- 
corded: (i)  Date,  (2)  name  of  cow,  (3)  pounds  of 
milk  given,  (4)  per  cent,  of  fat  in  milk,  (5)  lactometer 
reading,  if  desired. 

Calculating  results. — The  following  data  can  be  de- 
rived by  calculation  from  the  facts  recorded  above: 
(i)  Pounds  of  fat  produced  on  day  of  test,  (2)  pounds 
of  fat  and  milk  produced  each  month,  (3)  pounds  of 
fat  and  milk  produced  for  one  period  of  lactation. 

The  amount  of  fat  on  the  day  of  the  test  is  found 
by  multiplying  the  total  number  of  pounds  of  milk 
given  by  the  per  cent,  of  fat  found  and  dividing  by 
loo.  For  example,  if  the  day's  yield  of  milk  is  25 
pounds  and  the  per  cent,  of  fat  is  4,  the  day's  milk 
contains  i  pound  of  milk- fat.  (See  p.  193). 

The  amount  of  milk  and  fat  produced  each  month 


FARM    CONDITIONS  155 

is  found  as  follows,  when  the  test  is  made  once  in  two 
weeks :  Add  the  daily  yields  of  milk  for  the  day  of 
the  test  and  for  one  week  before  and  one  week  after 
the  test,  thus  obtaining  the  milk  yield  for  15  days. 
Multiply  this  sum  by  the  per  cent,  of  fat  found  on  the 
day  of  the  test  and  the  result  is  the  fat  yield  for  half 
a  month.  This  added  to  the  next  half  month  gives  the 
yield  of  fat  for  the  month. 

The  monthly  yields  of  milk  and  fat,  added  together 
at  the  end  of  the  period  of  lactation,  give  the  total 
yields  for  the  period. 

APPLICATION   OF   RESULTS   OF  TESTING  INDI- 
VIDUAL COWS 

A  progressive  dairyman  will  discard  from  his  herd 
any  animal  that  can  not  produce,  at  least,  200  pounds 
of  milk-fat  in  a  year,  especially  if  the  milk  is  sold  on 
the  basis  of  its  fat  content ;  and  he  will  aim,  by  means 
of  intelligent  breeding,  feeding  and  care,  to  increase 
the  annual  yield  of  milk-fat  to  250  or  300  pounds  for 
each  cow. 

TESTING  CREAM  ON  THE  FARM 

There  are  several  conditions  under  which  it  is  of 
advantage  to  test  cream  on  the  farm  in  order  to  know 
its  fat  content. 

When  a  dairyman  is  producing  cream  to  sell  directly 
to  consumers,  it  is  important  to  know  its  percentage 
of  fat,  in  order  that  it  may  be  uniform  from  day  to 
day,  whatever  the  desired  percentage  may  be.  The 
work  of  the  cream-separator  may  be  controlled  ad- 


156  MODERN    METHODS  OF  TESTING   MILK 

vantageously  only  by  knowing  the  percentage  of  fat 
in  the  cream  produced.  In  states  where  a  certain  per- 
centage of  fat  in  cream  is  required  by  law,  it  is  im- 
portant for  the  dairyman  to  know  that  his  product  is 
up  to  standard  before  he  sells  it. 

In  making  butter  on  the  farm,  better  results  can 
be  secured  by  having  the  cream  of  a  uniform  rich- 
ness in  fat,  and  the  percentage  of  fat  in  cream  can 
be  accurately  known  and  regulated  only  by  testing. 

TESTING  SKIM-MILK  AND  BUTTERMILK  ON 
THE  FARM 

The  completeness  with  which  fat  is  removed  from 
milk  by  different  methods  of  creaming,  whether  by 
separator  or  by  gravity  processes,  can  be  known  accu- 
rately only  by  testing  the  skim-milk  for  its  fat  content. 
With  the  knowledge  furnished  by  testing,  one  is  in 
position  to  prevent  further  losses  when  they  are  known 
to  exist.  Similarly,  the  efficiency  of  churning  may  be 
found  by  testing  the  buttermilk  for  its  fat  content. 

TESTING  MILK  AND   CREAM   FOR   SELF- 
PROTECTION 

"When  dairymen  sell  milk  or  cream  to  milk-dealers, 
creameries,  cheese-factories,  shipping-stations,  con- 
denseries,  etc.,  on  the  basis  of  the  per  cent,  of  fat  in 
milk,  it  is  often  a  matter  of  satisfaction  to  know  that 
the  tests  which  serve  as  a  basis  of  payment  are  cor- 
rect. If  a  dairyman  will  take  pains  to  acquire  the  skill 
necessary  to  perform  the  operations  of  the  Babcock 
test,  he  can  satisfy  himself  easily  in  regard  to  the  ac- 


FARM   CONDITIONS  157 

curacy  of  the  tests  of  his  milk  made  by  others.  In 
cases  where  a  purchaser  reports  the  test  lower  than 
it  is,  his  dishonesty  can  be  detected  by  means  of  home 
testing. 

It  is  also  important  for  the  dairyman  who  sells  milk 
directly  to  consumers  to  know  that  his  milk  is  above 
the  legal  standard.  Much  annoyance  and  expense  may 
sometimes  be  saved  by  knowing  the  percentage  of  fat 
and  solids  in  the  milk  one  sells. 


CHAPTER   XIII 

Methods  of  Commercial  Testing  and  Scoring 
of  Butter  and  Cheese 

In  commercial  transactions  in  butter  and  cheese, 
certain  points  or  qualities  have  been  adopted  as  a  basis 
or  standard  in  judging  the  commercial  value  of  these 
products.  The  terms  used  in  expressing  the  different 
qualities  vary  considerably  in  different  market  cen- 
ters, and  the  same  expression  is  used  with  different 
meanings  by  •  different  persons.  Frequently  individ- 
uals use  terms  that  are  strictly  local  or  personal.  It 
is  desirable  that  there  should  be  a  uniform  usage  and 
a  common  understanding  in  respect  to  the  terms  used 
in  judging  dairy  products.  The  attempt  is  made  here 
to  discuss  the  terms  in  common  use  and  to  define  them 
as  well  as  may  be,  in  the  hope  that  it  may  serve  as  a 
beginning  in  bringing  about  a  general  agreement  in 
respect  to  the  use  and  understanding  of  the  expres- 
sions employed  in  testing  and  scoring  dairy  products. 
The  definitions  here  given  can  hardly  be  expected  to 
be  in  full  agreement  with  the  usage  of  everyone,  since 
individuals  differ  from  one  another  so  much  in  their 
use  of  these  terms. 

SAMPLING  AND  TESTING  BUTTER 

In  obtaining  a  sample  of  butter  from  a  package  for 
examination,  a  butter-trier  (Fig.  52)  is  used.  This 
is  inserted  its  whole  length,  if  possible,  into  the  but- 

158 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE   159 

ter,  turned  around  once  and  then  drawn  out,  bringing 
with  it  a  long,  round  plug  as  a  sample.  The  plug,  as 
soon  as  drawn,  is  examined  for  flavor  by  smelling  and 
next  by  tasting.  It  is  then  broken  across 
to  examine  the  grain  or  texture,  and  then 
other  qualities  are  examined  in  turn. 

TERMS  USED  IN  DESCRIBING 
QUALITIES  OF  BUTTER 

The  qualities  that  have  been  selected 
to  sesve  as  a  basis  or  standard  in  the 
commercial  testing  and  scoring  of  but- 
ter are  as  follows:  (i)  Flavor,  (2)  tex- 
ture, (3)  body,  (4)  moisture,  (5)  color, 
(6)  salt  and  (7)  appearance. 

Flavor. — By  flavor  is  meant  the  qual- 
ity that  is  perceptible  to  the  senses  of 
smell  and  taste.  The  sense  of  smell  is, 
as  a  rule,  capable  of  being  developed  so 
as  to  be  more  highly  sensitive  than  the 
sense  of  taste  in  detecting  variations  of 
flavor.  The  flavor  in  normal  butter  is 
due  to  the  formation  of  certain  organic 
compounds  in  minute  quantities  during 
the  cream-ripening  process.  What  spe- 

..  BUTTER  TRIER 

cmc  compounds   these  are   has   not   yet 

been  learned.     The  odor  is  not  that  of  lactic  acid, 

since  that  is  odorless. 

Testing  Flavor. — The  flavor  is  obtained  by  placing 
the  plug  of  butter  under  the  nose  as  soon  as  possible 
after  the  plug  is  drawn.  A  portion  of  the  butter  is 
also  tasted. 


l6o  MODERN    METHODS  OF   TESTING   MILK 

Terms  describing  flavors. — The  following  terms 
are  selected  from  the  great  variety  of  names  that  are 
applied  to  various  flavors  found  in  butter:  (i)  Per- 
fect, (2)  quick,  (3)  clean,  (4)  light,  (5)  buttermilk, 
(6)  rancid,  (7)  tallowy,  (8)  cowy,  (9)  fishy,  (10) 
tainted,  (n)  stable,  (12)  weedy,  (13)  cheesy. 

(1)  Perfect  flavor  applies  to  butter  which  possesses 
the  characteristic  aroma  and  taste  of  high-grade  but- 
ter in  a  well-marked   degree.     It  is  difficult  to  de- 
scribe this  flavor  adequately,  but  it  is  commonly  char- 
acterized as  nutty,  clean,  pleasantly  aromatic,  delicate 
and  sweet.     Perhaps  the  best  description  of  it  is  to 
liken  it  to  the  flavor  of  clean,  well-ripened  cream.     It 
should  be  entirely  free  from  rancidity  or  any  unusual 
flavor. 

(2)  Quick  flavor  is  so  delicate  and  volatile  that  it 
disappears  quickly;  "high"  is  also  applied  to  the  same 
condition. 

(3)  Clean  flavor  is  free  from  every  trace  of  unpleas- 
ant aroma  or  taste. 

(4)  Light  or  Hat  flavor  in  butter  indicates  absence  of 
marked  flavor,  due  to  lack  of  cream-ripening,  to  ex- 
cessive washing  of  granules  and  to  other  conditions. 

(5)  Buttermilk  flavor  is  somewhat  sour  in  taste  and 
like  buttermilk  in  aroma.     It  is  due  to  the  presence  of 
an  excessive  amount  of  buttermilk  in  the  butter. 

(6)  Rancid  flavor  is  that  of  butyric  acid,  the  pres- 
ence of  which  is  due  to  the  use  of  over-aged  cream  or 
milk  or  to  age  of  butter,  in  which  butyric  acid  fer- 
mentation has  occurred.     When  the  flavor  is  strong, 
it  produces  an  unpleasant,  strangling  or  choking  sen- 
sation in  a  sensitive  throat.     The  odor  is  very  pene- 
trating and  lasting. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE   l6l 

(7)  Tallowy  flavor  is  like  that  of  tallow. 

(8)  Cowy  flavor  refers  to  the  animal  odor,  particu- 
larly as  noticed  in  the  breath  of  a  cow.     It  appears  to 
be  especially  prominent  in  cows  freshly  turned  into 
pasture. 

(9)  Fishy  odor  is  rather  suggestive  of  salted  cod- 
fish.   It  is  usually  due  to  a  special  form  of  fermentation 
appearing  in  the  milk  and  cream. 

(10)  Tainted  flavor  covers  a  variety  of  odors  and 
tastes  that  are  offensive  in  varying  degrees. 

(n)  Stable  flavor  is  the  one  characteristic  of  cow 
manure. 

(12)  Weedy  flavor  includes  such  abnormal  flavors  as 
may  come  from  onions,  leeks,  cabbages,  turnips,  etc. 

(13)  Cheesy  flavor  suggests  the  flavor  of  cheese  and 
is  due  to  fermentation  changes  in  the  proteid  of  but- 
ter; it  is  more  common  in  unsalted  butter. 

Texture. — The  texture  of  butter  refers  to  what  is 
called  the  grain  and  depends  upon  the  condition  of  the 
butter-granules.  In  its  first  formation  in  churning, 
butter  appears  in  very  small,  irregular  grains  or  gran- 
ules. These  grains  retain  their  individuality  in  large 
measure  throughout  the  rest  of  the  process  of  butter- 
making  and  even  in  the  finished  product.  The  more 
distinct  the  individuality  of  the  granules  can  be  kept 
in  making  the  butter  into  a  solid  mass,  the  better  is 
the  texture. 

Testing  texture. — The  granular  texture  of  butter 
is  seen  when  a  plug  or  chunk  of  butter  is  broken  into 
parts  transversely,  giving  somewhat  the  fractured  ap- 
pearance seen  in  broken  steel  and  free  from  a  smooth, 
greasy  appearance.  Another  method  of  testing  tex- 


162  MODERN    METHODS    OF   TESTING    MILK 

ture  is  to  pass  a  knife-blade  or  butter-trier  through 
the  butter;  when  it  is  withdrawn,  the  trier  is  clean 
and  free  from  any  greasy  appearance,  if  the  texture 
is  good. 

Terms  describing  texture. — The  terms  used  to  de- 
scribe texture  are  (i)  perfect,  (2)  poor  grain,  and 
(3)  salvy. 

1 i )  Perfect  texture  in  butter  is  shown  by  the  gran- 
ular formation,  as  described  above. 

(2)  Poor  grain  texture  in  butter  is  shown  by  less 
marked  grain  and  a  more  or  less  smooth,  greasy  ap- 
pearance on  the  broken  surfaces. 

(3)  Salvy  texture  applies  to  butter  in  which  the 
grain  is  more  or  less  destroyed  and  the  smooth,  greasy 
appearance  of  the  broken  surface  is  very  marked. 

Defective  texture  in  butter  is  caused  by  allowing 
the  butter-granules  in  the  churn  to  become  too  large 
and  by  working  too  much  or  at  too  high  a  tempera- 
ture. The  granular  texture  of  butter  is  completely  de- 
stroyed by  warming  butter  to  near  its  melting  point. 

Body. — By  this  term  is  meant  the  quality  of  consis- 
tency, firmness  or  hardness,  as  shown  by  not  melting 
or  softening  too  easily. 

Testing  body. — The  body  of  a  sample  of  butter  can 
be  ascertained  by  pressing  a  portion  of  the  plug  be- 
tween the  thumb  and  fingers,  and  also  by  pressing  be- 
tween the  tongue  and  roof  of  the  mouth. 

Terms  describing  body. — The  terms  used  to  de- 
scribe the  body  of  butter  are:  (i)  perfect,  firm  or 
solid,  (2)  hard  or  tallowy,  (3)  weak-bodied,  (4) 
sticky. 


COMMERCIAL  TESTING  OF   BUTTER  AND  CHEESE   163 

(1)  Perfect  body  in  butter  is  shown  by  firmness  or 
solidity  under  proper  conditions  of  temperature.  When 
pressed  between  the  ringers  or  on  the  tongue  it  shows 
a  certain  amount  of  resistance. 

(2)  Hard  or  tallowy  body  is  shown  by  excessive  so- 
lidity, being  characteristic  of  butter  made  from  cows 
far  along  in  lactation,  or  in  the  case  of  cows  heavily 
fed  on  cotton-seed  meal. 

(3)  Weak-bodied  butter  is  lacking  in  firmness,  more 
or  less  soft,  melting  more  easily  on  warming  than  a 
perfect-bodied  butter.     Weak-bodied  butters  are  usu- 
ally salvy  in  texture  and  high  in  moisture.     Certain 
feeds,  such  as  gluten  meal,  tend  to  increase  the  soft- 
ness of  butter. 

(4)  Sticky  body  in  butter  is  shown  by  extreme  soft- 
ness amounting  to  stickiness. 

Moisture. — The  water  in  butter  should  be  so  thor- 
oughly incorporated  with  the  fat  that  it  does  not  appear 
in  the  form  of  free  beads  of  water  visible  to  the  eye. 
Water  should  not  run  off  the  trier  when  a  sample  is 
drawn.  The  water  should  also  be  clear  and  trans- 
parent. 

Testing  moisture. — The  sample  of  butter  is  exam- 
ined for  the  appearance  of  moisture  or  brine  in  respect 
to  the  completeness  of  its  incorporation  and  its  clear- 
ness. 

Terms  describing  moisture. — The  following  terms 
are  used  to  describe  the  condition  of  moisture  in  but- 
ter: (i)  Perfect,  (2)  excessive,  (3)  milky  or  turbid. 

(1)  Perfect  moisture  in  butter  is  shown  by  the  ab- 
sence of  any  visible  moisture  in  the  form  of  drops. 

(2)  Excessive  moisture  is  shown  by  the  presence  of 


164  MODERN    METHODS    OF    TESTING    MILK 

water  easily  apparent  to  the  eye.  Butter  may  some- 
times contain  so  much  water  as  to  be  called  "mushy." 

(3)  Milky  or  turbid  moisture  or  brine  appears  more 
or  less  milky,  being  due  to  the  presence  of  too  much 
buttermilk. 

Relation  of  texture,  body  and  moisture. — Considera- 
ble confusion  prevails  in  the  use  of  the  terms  texture, 
body  and  moisture.  Some  use  the  term  texture  to  in- 
clude also  body  and  moisture;  others  use  the  term 
body  to  include  texture,  while  others  use  the  expres- 
sion "body  and  grain"  to  cover  all  three  qualities.  Tex- 
ture and  body  and  moisture  may  be  influenced  by  the 
same  conditions  and  may  be,  to  some  extent,  interde- 
pendent, but  in  reality  they  are  distinct  properties  and, 
if  they  were  treated  as  such,  needless  confusion  would 
be  avoided. 

Color. — The  color  of  butter  varies  in  different  mar- 
kets according  to  requirements,  but  most  of  the  but- 
ter made  in  the  United  States  has,  as  its  standard,  an 
even,  bright,  straw-yellow.  Most  butter  in  commerce 
is  colored  artificially,  so  as  to  maintain  a  uniform  ap- 
pearance at  all  seasons  of  the  year.  Somewhat  dif- 
ferent shades  of  color  are  demanded  by  different  mar- 
kets. 

Testing  color. — The  quality  of  color  is  tested 
simply  by  inspection  with  the  eye.  The  thumb-nail  is 
run  along  the  surface  of  the  plug  near  the  edge  of  the 
trier,  and  the  fresh  surface  thus  made  is  examined. 
The  examiner  carries  in  his  mind  the  shade  of  what 
he  regards  as  an  ideal  color  and  judges  the  sample 
under  examination  by  its  comparison  with  his  ideal. 
It  would  lead  to  easier  methods  of  comparison  and 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE    165 

more  uniform  results  if  there  could  be  agreed  upon 
a  certain  shade  of  color  which  should  serve  as  a  na- 
tional standard  as  far  as  possible.  Such  a  color  stand- 
ard could  be  furnished  butter-makers  and  examiners 
of  butter.  Along  with  such  a  standard  color,  there 
could  be  prepared  a  scale  of  shades  which  could  serve 
as  a  basis  for  scoring  color. 

Terms  describing  color. — The  terms  used  in  de- 
scribing the  color  of  butter  are.:  (i)  perfect,  (2)  light, 
(3)  high,  (4)  reddish,  (5)  mottled,  and  (6)  white- 
specked. 

1 i )  Perfect  color  in  butter  is  a  straw-yellow,  bright, 
and  uniform  throughout  the  mass.     A  plug  of  butter 
held  between  the  light  and  the  eye  should  be  evenly 
translucent  and  not  opaque  or  cloudy. 

(2)  Light  color  is  shown  by  insufficient  color,  the 
yellow  being  too  pale. 

(3)  High  color  is  deeper  yellow  than  called  for  by 
perfect  color. 

(4)  Reddish  color  is  self-explanatory  and  is  due  to 
excessive  use  of  coloring  material. 

(5)  Mottled  color  in  butter  is  shown  by  the  appear- 
ance of  light-colored  portions,  which  may  be  in  spots 
or  streaks  or  waves.    The  term  wavy  is  often  used  to 
indicate  a  variation  of  color  that  is  just  perceptible. 
They  are  not  seen  as  readily  on  a  sample  plug  drawn 
by  a  trier  as  they  can  be  by  cutting  a  lump  of  butter 
across  so  as  to  show  a  smooth,  broad  surface.    Slight 
mottling  is  apt  to  escape  observation  when  the  exam- 
ination is  made  only  of  a  plug.     Mottling  is  due  to 
the  action  of  salt  upon  buttermilk  retained  in  the  but- 
ter.    The  light  portions  owe  their  color  to  the  pres- 


l66  MODERN    METHODS   OF    TESTING    MILK 

ence  of  the  casein  lactate  of  buttermilk.  Removal  of 
buttermilk  from  the  butter-granules  prevents  mottling. 
(Bulletin  No.  263,  N.  Y.  Agr.  Exp.  Sta.  1905). 

(6)  White-specked  color  in  butter  appears  in  white 
specks  of  varying  size,  but  usually  small.  They  are 
due  to  particles  of  coagulated  casein  lactate  produced 
in  cream  by  over-ripening,  arid  also  to  dried  cream 
particles,  caused  by  lack  of  stirring  during  the  process 
of  ripening.  • 

Salt. — The  amount  of  salt  in  butter  varies  with  dif- 
ferent markets;  but,  whatever  the  amount  used,  it 
should  be  completely  dissolved  and  evenly  distributed 
through  the  mass  of  butter. 

Testing  butter  for  salt. — The  quality  of  butter  as 
affected  by  salt  is  examined  by  tasting,  sight  and  feel- 
ing. Undissolved  particles  of  salt,  when  they  can  not 
be  felt  on  the  tongue  or  seen,  can  be  detected  by  rub- 
bing some  of  the  butter  between  the  fingers. 

Terms  describing  salt. — The  terms  used  in  de- 
scribing the  quality  of  butter  in  relation  to  salt  are  the 
following:  (i)  Perfect,  (2)  too  salty,  (3)  flat,  (4) 
gritty,  (5)  uneven. 

(1)  Perfect  quality  in  respect  to  salt  in  butter  is 
shown  as  follows :    The  salt  must  be  in  the  proportion 
demanded  by  the  market ;  it  must  be  entirely  dissolved 
and  evenly  distributed. 

(2)  Too  salty  butter  contains  more  salt  than  the 
market  demands. 

(3)  Flat  butter  is  lacking  in  salt  for  the  market  re- 
quirements. 

(4)  Gritty  butter  contains  undissolved  salt. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE   167 

(5)  Uneven  salt  in  butter  is  lack  of  uniformity,  some 
portions  of  butter  being  more  salty  than  others. 

Appearance. — Under  this  head  are  included  the 
manner  of  packing,  the  attractive  appearance  of  the 
package,  cleanliness,  etc. 

testing  appearance. — When  the  cover  of  the  pack- 
age is  removed  for  sampling  the  butter,  the  appearance 
of  the  surface  of  the  butter  is  noticed.  The  outside  of 
the  package  is  also  examined.  The  two  general  quali- 
ties that  must  be  kept  in  mind  in  this  connection  are 
cleanliness  and  neatness. 

Terms  describing  appearance. — The  quality  of  ap- 
pearance of  butter  may  be  considered  under  two  heads, 
(i)  finish  and  (2)  package. 

1 i )  Finish  in  appearance,  in  connection  with  exam- 
ining butter,  refers  to  the  manner  of  packing.     The 
finish  is  perfect  when  the  package  is  lined  with  paraf- 
fin or  with  a  good  quality  of  parchment  paper,  neatly 
placed,  and  the  package  well  filled,  the  surface  being 
even  and  bright.     The  package  should  be  just  evenly 
full.     The  top  should  be  neatly  covered  with  cheese- 
cloth saturated  with  brine. 

(2)  Package.— The  package  is  regarded  as  perfect 
when  of  good  material,  well-made,  clean,  and  neat  in 
appearance.     In  the  same  lot  of  butter  the  packages 
should  all  be  alike  in  size  and  shape. 

SCORING  BUTTER 

The  different  qualities  indicated  above  are  used  in 
a  specific  manner  for  judging  and  fixing  the  com- 
mercial value  of  butter. 


l68  MODERN    METHODS    OF    TESTING    MILK 

Scale  of  points. — To  each  quality  is  assigned  a  defi- 
nite numerical  value  and  these  numbers  are  called  a 
scale  of  points.  The  following  scale  of  points  is  in 
common  use  in  many  markets  of  this  country,  the  num- 
bers indicating  perfect  quality  in  each  case,  and  the 
totals  aggregating  100: 

Flavor,  45  points.  Color,  15  points. 

Texture,  (10)    )  Salt,  10  points. 

Body,   (10)         [-25  points.  Appearance,  5  points. 

Moisture,  (5)    )  Total,          100  points. 

Method  of  scoring. — In  scoring  a  sample  of  but- 
ter, an  examination  is  made  with  reference  to  each  of 
the  qualities  mentioned.  In  those  qualities  in  which  it 
is  perfect,  it  is  given  the  values  or  points  assigned 
above.  If  the  butter  is  defective  in  any  quality,  that  is, 
short  of  perfect,  then  a  smaller  value  is  given  than  the 
one  indicated  above  in  the  scale  of  points ;  the  more  de- 
fective the  butter  is  in  any  quality,  the  lower  is  the 
value  or  number  of  points  given  it.  When  all  the 
qualities  have  been  scored,  the  numbers  of  points  as- 
signed to  them  are  added  and  the  total  is  the  score  of 
the  butter  under  examination. 

It  can  readily  be  seen  that  judgment,  trained  by  ex- 
perience, is  required  to  assign  to  each  quality  its  proper 
number  of  points.  The  sense  of  smell  and  of  taste 
must  be  highly  developed  by  training  in  the  field  of 
experience.  The  eye  and  touch  must  also  be  trained 
by  special  experience. 

Score-cards. — For  convenience,  score-cards  are  used 
in  keeping  records  of  the  results  of  scoring  where  many 
samples  are  examined.  The  following  form  illustrates 
a  commercial  score-card: 


COMMERCIAL  TESTING  OF   BUTTER  AND  CHEESE   169 


NAME  OR  NUMBER  IDENTIFYING  SAMPLE, 
DATE JUDGE 


QUALITY 

SCORE-POINTS 

Sample 
1 

Sample 
2 

Sample 
3 

Sample 
4 

Flavor 

45 

45 

40 

36 

32 

Texture         

10 

g 

10 

8 

7 

Body... 

10 

10 

8 

g 

Moisture  

5 

5 

3 

4 

4 

Color 

15 

13 

14 

13 

12 

Salt 

10 

10 

10 

10 

3 

Appearance 

5 

4 

5 

4 

5 

95 

90 

83 

75 

These  scores,  under  the  system  of  grading  described 
below,  would  be  graded  as  follows:  Sample  i,  "ex- 
tras;" sample  2,  "firsts;"  sample  3,  "seconds;"  and 
sample  4,  "thirds." 

In  commerical  scoring,  reasons  for  the  number  of 
points  given  are  not  stated  ;  but  in  dairy  schools  and 
competitive  public  exhibitions,  where  educational  pur- 
poses are  in  view,  the  reason  for  each  score  should  be 
given.  The  following  form  of  score-card  for  such 
purposes  is  a  suggestion,  which  may  be  modified  to 
suit  any  special  conditions: 

Butter-Scoring  —  Numerical   and    Descriptive   Card 
Date  .............. 


Name  or  number  identifying  butter 


MODERN    METHODS    OF   TESTING    MILK 


NUMERICAL  SCORE. 

Perfection— Flavor,    Texture,    Body,   Moisture,   Color,   Salt,    Appearance 
(45)  (10)  (10)  (5)  (15)        (10)  (5) 

Score  given       — 

DESCRIPTIVE  SCORE  (check  defects  below). 


Flavor 

Texture 

Body 

Moisture 

Color 

Salt 

Appear- 
ance 

Perfect    Quick 

Perfect 

Perfect 

Perfect 

Perfect 

Perfect 

Finish 

Clean     Ught 

Buttermilk 
Rancid 

Tallowy* 
Cowy 

POOT- 
grain 

Salvy 

Firm 
Hard 

Weak- 
bodied 

Exces- 
sive 

Milky 

Ivight 
High 
Reddish 

Too  salty 
Flat 
Gritty 

Package 

Fishy  Tainted 

Sticky 

Mottled 

Uneven 

Stable  Weedy 
Cheesy 

Wavy 
Specks 

CLASSES  AND  GRADES  OF  BUTTER 

The  following  system  for  classifying  and  grading 
butter  is  taken  from  the  regulations  of  the  New  York 
Mercantile  Exchange : 
Classification : — 

1.  Creamery  Butter  includes  butter  made  in  a  cream- 
ery from  cream  obtained  by  the  separator  system,  or 
from  gathered  cream. 

2.  Imitation     Creamery     Butter     includes     butter 
churned  by  the  dairyman,  collected  in  its  unsalted,  tin- 
worked  condition,  and  worked,  salted  and  packed  by 
the  dealer  or  shipper. 

3.  Dairy  Butter  includes  such  as  is  made,   salted 
and  packed  by  the  dairyman  and  offered  in  its  orig- 
inal package. 

4.  Factory  Butter  is  butter  collected  in  rolls,  lumps, 


COMMERCIAL  TESTING  OF   BUTTER  AND   CHEESE    I/I 

or  in  whole  packages,  and  reworked  by  the  dealer  or 
shipper. 

5.  Renovated  Butter  is  that  made  by  taking  pure 
butter  and  melting  the  same  and  rechurning  with  fresh 
milk,    cream   or   skim-milk,   or  other   equivalent   pro- 
cess. 

6.  Grease   consists   of   all   grades   of  butter   below 
Fourths  free  from  adulteration. 

7.  Known  Marks  is  a  term  used  to  include   such 
butter  as  is  known  to  the  trade  under  some  particular 
mark  or  designation  and  must  grade   as   Extras,   if 
creamery,  and  as   Firsts,  if  reworked  butter,  in  the 
season  in  which  it  is  offered,  unless  otherwise  speci- 
fied. 

Grades: — Grades  of  butter  must  conform  to  all 
the  following  requirements  and  are  not  determined  by 
score  alone. 

1.  Extras  must  be  of  the  highest  grades  of  butter 
made  in  the  season  when  offered  under  the  different 
classifications ;  90  per  cent,  shall  be  up  to  the  following 
standard  and  the  balance  must  not  grade  below  Firsts : 

(i)Flavor  must  be  fine,  sweet,  clean  and  fresh,  if 
of  current  make;  and  fine,  sweet  and  clean,  if  held. 
(2)  Body  must  be  firm,  smooth  and  uniform.  (3) 
Color  should  be  a  light  straw  shade,  even  and  uniform. 
(4)  Salt  should  be  medium.  (5)  Package  should  be 
good,  uniform  and  clean.  (6)  Score  must  average  93 
points  or  higher. 

2.  Firsts  is  a  grade  just  below  Extras  and  must 
be  fine  butter  for  the  season  when  made  and  offered, 
under  the  different  classifications,  and  up  to  the  fol- 
lowing standard: 


172  MODERN    METHODS  OF  TESTING   MILK 

(i)  Flavor  must  be  good,  sweet,  clean  and  fresh, 
if  of  current  make ;  and  good,  sweet  and  clean,  if  held. 
(2)  Body  must  be  good  and  uniform.  (3)  Color  must 
be  reasonably  uniform,  neither  too  high  nor  too  light. 

(4)  Salt  should  be  medium.  (5)   Packages  should  be 
good  and  uniform.  (6)  Score  must  average  87  points 
or  higher. 

3.  Seconds  is  a  grade  just  below  Firsts  and  must 
be  good  for  the  season  when  offered  under  the  differ- 
ent classifications,  and  up  to  the  following  standard : 

(i)  Flavor  must  be  reasonably  good  and  sweet.  (2) 
Body,  if  creamery  or  dairy,  must  be  solid-boring.  If 
factory  or  renovated,  must  be  90  per  cent,  solid-bor- 
ing. (3)  Color  must  be  fairly  uniform.  (4)  Salt  may 
be  high,  medium  or  light.  (5)  Package  should  be 
good  and  uniform.  (6)  Score  must  average  80  points 
or  higher. 

4.  Thirds  is  a  grade  just  below  Seconds. 

( i )  Flavor  must  be  reasonably  good ;  may  be  strong 
on  top  and  sides.  (2)  Body  should  be  fair-boring,  if 
creamery  or  dairy,  and  at  least  50  per  cent,  boring  a 
full  trier,  if  factory  or  renovated.  (3)  Color  may  be 
irregular.  (4)  Salt  may  be  high,  light  or  irregular. 

(5)  Packages   should  be   fairly   uniform.    (6)    Score 
must  average  75  points  or  higher. 

5.  Fourths  is  a  grade  just  below  Thirds  and  may 
consist  of  promiscuous  lots. 

( i )  Flavor  may  be  off  and  strong  on  tops  and  sides. 
(2)  Body  is  not  required  to  draw  a  full  trier.  (3) 
Color  may  be  irregular.  (4)  Salt  may  be  high,  light, 
or  irregular.  (5)  Package  may  be  of  any  kind  men- 
tioned at  time  of  sale. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE    173 

SAMPLING  AND  TESTING  CHEESE 

Only  the  ordinary  American  cheese,  usually  made 
by  the  cheddar  system,  is  here  considered.  For  com- 
mercial testing,  cheese  is  sampled  by  a  cheese-trier 
in  much  the  same  manner  as  butter.  The  plug  should 
always  be  drawn  from  the  top  and  not  from  the  side 
in  order  to  avoid  injuring  the  protective  power  of  the 
bandage.  The  plug  drawn  is  examined  by  smelling, 
feeling,  appearance,  etc.,  in  reference  to  the  various 
qualities  mentioned  below. 

TERMS  USED  IN  DESCRIBING  QUALITIES  OF 
CHEESE 

The  following  qualities  have  been  selected  to  serve 
as  a  basis  in  the  commercial  testing  and  scoring  of 
cheese:  (i)  Flavor,  (2)  texture,  (3)  body,  (4)  color, 
(5)  salt,  and  (6)  appearance. 

Flavor. — By  flavor  is  meant  the  quality  that  is  per- 
ceptible to  the  smell  and  taste.  The  sense  of  smell  is 
depended  upon  in  testing  flavor  in  cheese  much 
more  largely  than  is  the  sense  of  taste,  because,  in  ex- 
amining a  large  number  of  samples  of  cheese  in  suc- 
cession, constant  tasting  soon  dulls  not  only  the  sense 
of  taste  but  also  that  of  smell.  Flavor  in  cheese  is 
due  to  the  formation  of  some  unknown  compound  or 
compounds  during  the  ripening  process. 

Testing  flavor  in  cheese. — The  flavor  is  best  ob- 
tained by  direct  smelling  of  the  plug  as  soon  as  it  is 
drawn  and,  in  addition,  by  crushing  and  warming 
some  of  the  cheese  in  the  hand  and  then  smelling. 

Terms  used  in  describing  cheese  flavors. — From 
a  great  variety  of  names  applied  to  various  flavors 


174  MODERN    METHODS   OF  TESTING    MILK 

found  in  cheese,  the  following  terms  are  selected  for 
consideration:  (i)  Perfect,  (2)  high  or  quick,  (3) 
clean,  (4)  low  or  flat,  (5)  strong,  (6)  too  much  acid, 
(7)  too  little  acid,  (8)  sour,  (9)  sweet  or  fruity,  (10) 
rancid,  (n)  tallowy,  (12)  tainted,  (13)  stable,  (14) 
weedy,  (15)  bitter,  (16)  cowy. 

(1)  Perfect  flavor  applies  to  cheese  when  it  some- 
what resembles  that  of  first-class  butter  with  an  added 
quality  of  its  own  that  is  characteristic  but  cannot  be 
described   further   than   to   call   it   cheese-like.      It   is 
sometimes  described  as  "nutty."     This  flavor  should 
be  marked,  but  not  strong.     It  should  be   free  from 
all  other  flavors,  particularly  the  more  or  less  offen- 
sive products  of  undesirable  fermentations.     The  taste 
should  be  mild  and  somewhat  lasting,  but  should  not 
be  so  sharp  as  to  "bite"  the  tongue. 

(2)  High  or  quick  flavor  is  a  delicate  flavor  that  dis- 
appears quickly. 

(3)  Clean  flavor  is  free  from  every  trace  of  unpleas- 
ant aroma  or  taste. 

(4)  Low  or  Hat  flavor  applies  to  slight  traces,  or 
absence,  of  flavor;  it  is  insipid. 

(5)  Strong  flavor  is  a  good  flavor  very  pronounced 
but  free  from  everything  offensive ;  it  is  a  good  flavor 
strongly  developed. 

(6)  Too  much  acid  applies  to  flavor  that  smells 
somewhat  sour  but  does  not  taste  sour. 

(7)  Too  little  acid  applies  to  a  mild  flavor,  lacking 
in  character. 

(8)  Sour  flavor  is   characterized  by  a   sour  taste 
when  the  cheese  is  fresh,  owing  to  the  presence  of  too 
much  whey. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE    1/5 

(9)  Sweet  or  fruity  flavor  is  suggestive  of  artificial 
pineapple  odor  and  is  somewhat  "sickish." 

(10)  Rancid  flavor  is  that  of  butyric  acid,  more  com- 
mon in  old  cheese  than  in  young.    When  very  strong, 
it  affects  a  delicate  throat  with  a  slight  sensation  of 
choking  or  strangling. 

(n)  Tallowy  flavor  is  like  that  of  tallow. 

(12)  Tainted   flavor   includes   a   variety   of   odors, 
mildly  to  strongly  offensive. 

(13)  Stable  flavor  suggests  the  smell  of  cow<  ma- 
nure. 

(14)  Weedy  flavor  applies  to  such  abnormal  flavors 
as  come  from  onions,  leeks,  cabbages,  ragweed,  etc. 

(15)  Bitter  flavor  is  self-descriptive.    It  is  often  due 
to  certain  fermentations  that  develop  when  a  cheese 
is  undersalted. 

(16)  Cowy  flavor  is  suggestive  of  the  breath  of  a 
cow  and  may  develop  in  cheese  from  some  form  of 
fermentation. 

Texture. — Texture,  as  applied  to  cheese,  refers 
chiefly  to  compactness  or  appearance  of  solidity,  and 
has  a  meaning  quite  different  from  what  it  has  when 
used  with  reference  to  butter.  It  is  quite  common  to 
regard  the  "body"  as  a  part  of  the  texture,  but  the 
two  qualities  are  clearly  distinct. 

Testing  texture  in  cheese. — The  texture  of  cheese 
is  tested  by  an  examination  of  the  plug  with  reference 
to  the  presence  of  holes.  The  plug  is  broken  in  two 
and  the  broken  ends  examined  for  the  characteristic 
flinty  appearance. 

Terms  describing  texture. — The  following  terms 
are  among  those  most  commonly  used  in  describing 


176  MODERN    METHODS   OF   TESTING    MILK 

texture:  (i)   Perfect,   (2)   close,   (3)   loose,   (4)   me- 
chanical holes,  (5)  gas  or  pin-holes,  (6)   Swiss  holes. 

1 i )  Perfect  texture  in  cheese  is  shown  when  a  plug 
or  a  cut  surface  of  the  inside  of  the  cheese  presents 
to  the  eye  a  solid,   compact,   continuous   appearance, 
free  from  breaks,  holes  and  chunks.     When  a  plug 
is  broken  in  two,  it  should  show  a  flaky  appearance, 
termed   a   "flinty"   break,   resembling   the   surface   of 
broken  flint  or  steel. 

(2)  Close   texture   describes   the   appearance   of   a 
cut  surface  of  cheese   when   free   from   all   kinds   of 
holes. 

(3)  Loose  or  porous  texture  is  indicated  by  lack  of 
solid  compactness,  being  more  or  less   full  of  holes, 
which  vary  from  a  few  to  enough  to  make  a  spongy 
appearance. 

(4)  Mechanical  holes  in  cheese  are  irregular,  open 
spaces,   caused   by   the   incomplete   cementing   of   the 
pieces  of  curd  in  the  press. 

(5)  Gas-holes  or  pin-holes  are  small  holes,  produced 
by  gaseous  products  of  fermentation. 

(6)  Swiss  holes  are  fairly  large,  round  holes,  such 
as  are  present  in  Emmenthaler  cheese. 

Body. — This  term,  used  in  connection  with  cheese, 
refers  to  the  consistency,  firmness  or  substance  of 
cheese.  It  is  largely  influenced  by  the  amount  of 
fat  and  moisture  in  cheese. 

Testing  body. — This  quality  is  found  by  pressing  a 
piece  of  cheese  between  the  thumb  and  fingers. 

Terms  describing  body. — The  following  terms  are 
among  those  used  in  describing  the  body  of  cheese: 
(i)  Perfect,  (2)  solid  or  firm,  (3)  smooth,  (4)  silky, 
(5)  waxy,  (6)  pasty  or  salvy,  (7)  stiff,  corky,  or 


COMMERCIAL  TESTING  OF   BUTTER  AND  CHEESE    177 

curdy,  (8)  weak-bodied,  (9)  mealy,  (10)  gritty,  (n) 
watery,   (12)   over-dry. 

1 i )  Perfect  body  in  cheese  is  indicated  when  it  feels 
solid,  firm  and  smooth  in  its  consistency  or  substance. 
It  does  not  crumble  under  pressure.     A  plug  drawn 
from  a  cheese  of  perfect  body  should  be  smooth  in  ap- 
pearance and  not  "fuzzy." 

(2)  Solid  or  firm  body  is  indicated  when  cheese  of- 
fers a  certain  amount  of  resistance  under  pressure, 
somewhat  like  that  shown  by  a  piece  of  fat  pork  or 
cold  butter.     The  term  meaty  is  also  used. 

(3)  Smooth-bodied  cheese,  when  pressed  between 
the  thumb  and  fingers,  feels  smooth  and  velvet-like,  as 
distinct  from  harsh,  gritty  or  mealy. 

(4)  Silky-bodied  cheese  is  smooth  in  feeling  but  not 
over-solid  in  consistency. 

(5)  Waxy-bodied  cheese  is  much  the  same  as  silky 
but  possessing  more  firmness  or  solidity. 

(6)  Pasty  or  salvy  cheese  is  very  soft,  usually  from 
an  excess  of  moisture.     When  pressed,  it  sticks  to  the 
fingers. 

(7)  Stiff,  corky  or  curdy  cheese  is  hard,  tough,  over- 
firm  ;  it  does  not  crush  down  readily  when  pressed  in 
the  hand. 

(8)  Weak-bodied   cheese   is   very   soft,   lacking   in 
firmness  but  not  necessarily  sticky  like  pasty  cheese. 

(9)  Mealy  cheese  breaks  down  in  fine  crumbs  when 
pressed. 

(10)  Gritty-bodied   cheese   feels  harsh  and  gritty 
under  pressure. 

( 1 1 )  Watery-bodied  cheese  is  excessively  soft,  pasty 
and  sticky. 


1^8  MODERN    METHODS   OF   TESTING    MILK 

(12)  In  an  over-dry  cheese  the  body  is  very  hard 
or  mealy. 

Color. — The  color  of  cheese  varies  considerably, 
whether  artificially  colored  or  not.  There  appears  to 
be  an  increasing  demand  for  uncolored  cheese.  The 
coloring  varies  fronj  a  pale  yellow  to  a  reddish  yel- 
low, according  to  the  demands  of  special  markets. 

Testing  color. — The  color  is  tested  by  inspection 
with  the  eye,  the  examiner  noticing  particularly  unev- 
enness  and  any  extreme  condition  of  color. 

Terms  describing  color. — Color  in  cheese  is  de- 
scribed by  the  following  terms:  (i)  Perfect,  (2) 
straight,  (3)  translucent,  (4)  white  specks,  (5)  streak- 
ed, (6)  wavy,  (7)  mottled,  (8)  acid-cut,  (9)  high, 
(10)  light,  (n)  uncolored. 

(1)  Perfect  color  in  cheese  is  indicated  by  evenness 
of  color  throughout  the  mass.     A  plug  held  between 
the  eye  and  light  should  appear  somewhat  translucent. 

(2)  Straight  color  is  an  even,  uniform  color  through 
the  whole  cheese. 

(3)  Translucent  applies  to  color  in  cheese   which 
appears  slightly  translucent  when  the  plug  is  held  be- 
tween the  eye  and  the  light. 

(4)  White  specks  is  a  term  that  describes   itself. 
Such  specks  in  cheese  are  a  defect.    They  may  appear 
in  cheese  cured  at  low  temperature. 

(5)  Streaked  color  indicates  that  there  are  light- 
colored  portions  in  the  form  of  streaks. 

(6)  Wavy  color  applies  to  lighter  portions  appear- 
ing in  the  form  of  waves. 

(7)  Mottled  color  shows  in  cheese  in  lighter-colored 
spots  of  fairly  large  size,  more  or  less  irregular. 


COMMERCIAL  TESTING  OF  BUTTER  AND  CHEESE  179 

(8)  Acid-cut  color  is  shown  in  cheese  when  consid- 
erable portions  of  the  cheese  have  been  made  lighter 
in  color  by  the  presence  of  too  much  acid  (whey). 

(9)  High   color   is   indicated   by   a   reddish   color, 
caused   by   using  too   much   coloring  matter.      How- 
ever, the  question  of  color  is  a  relative  one,  because 
the  demand  in  different  markets  varies  from  uncolored 
to  extremely  high  color. 

(10)  Light  color  is  the  term  usually  used  in  describ- 
ing cheese  that  has  been  made  uniformly  dead  white 
by  the  action  of  too  much  acid  (whey). 

(n)  Uncolored  cheddar  cheese  is  not  white  but  of 
a  light  amber  shade. 

Salt. — The  amount  of  salt  in  cheese  varies  somewhat 
with  different  markets.  There  is  seldom  experienced 
difficulty  of  uneven  salting  in  cheese,  because  the  salt 
slowly  permeates  the  cheese  in  the  ripening  process. 
Little  variations  usually  occur  in  different  parts  of 
the  same  cheese,  but  are  so  slight  as  to  be  incapable  of 
being  noticed  by  ordinary  methods  of  examination. 

Testing  cheese  for  salt. — The  quality  of  cheese  as 
influenced  by  the  salt  is  found  simply  by  tasting. 

Terms  used  in  describing  salt. — In  describing  the 
relation  of  salt  to  cheese,  the  following  terms  are  used : 
(i)  Perfect,  (2)  too  much,  (3)  too  little. 

(1)  Perfect   applies    to    salt   in    cheese    when    just 
enough  has  been  used  to  impart  a  sufficient  taste  of 
salt. 

(2)  Too  much  salt  is  indicated  by  salty  taste.     Too 
much  salt  in  cheese  causes  a  dry,  mealy  texture,  over- 
firm  body  and  imperfect  flavor. 

(3)  Too  little  salt  is  shown  by  insipidity  of  taste. 


ISO  MODERN    METHODS   OF  TESTING   MILK 

It  is  usually  accompanied  by  bitter  flavor  and  porous 
texture. 

Appearance.— This  term  refers  to  the  general  ap- 
pearance of  the  cheese  to  the  eye  in  respect  to  uni- 
formity, neatness  and  cleanliness.  It  may  also  include 
the  boxing.  One  system,  as  in  the  case  of  butter,  de- 
scribes under  "finish"  the  appearance  of  the  cheese,  and 
under  "packages"  the  boxing;  and  we  will  follow  this 
method  here. 

Testing  appearance. — When  the  cover  of  the  box 
is  removed  for  sampling,  in  the  case  of  boxed  cheese, 
the  appearance  of  the  cheese  is  noticed  and  the  box 
itself  is  examined.  Cleanliness  and  neatness  are 
the  points  to  observe  in  judging  appearance. 

Terms  describing  appearance. — The  general  terms 
used  in  describing  appearance  are  (i)  finish  and  (2) 
package. 

(1)  Finish  in  appearance,  in  order  to  be  perfect, 
must  meet  the  following  requirements :  The  rind  must 
be  smooth,  even  in  color,  free  from  cracks  and  fairly 
hard.     The  bandage  must  be   without  wrinkles   and 
must  be  neatly  rounded  over  the  edges  about  an  inch 
and  a  half  on  each  end  of  the  cheese.     The  sides  of 
the  cheese  should  be  straight  and  of  uniform  height 
all  around. 

The  faults  of  appearance  in  finish  are  as  follows,  the 
terms  being  self-descriptive:  (i)  Cracks,  (2)  light 
spots,  (3)  roughness  in  rind,  (4)  uneven  edges,  (5) 
wrinkles  in  bandage,  (6)  lack  of  uniformity  in  ends 
and  in  height,  (7)  bulging  out  at  sides  or  ends. 

(2)  Package. — The  packages  or  boxes  are  regarded 
as  perfect  when  of  good  material,  well  made,  strong, 


COMMERCIAL  TESTING  OF  BUTTER  AND   CHEESE    l8l 

clean,  close-fitting,  uniform  in  size  and  in  undamaged 
condition. 

SCORING  CHEESE 

The  qualities  described  in  the  preceding  pages  are 
used  for  judging  and  fixing  the  commercial  value  of 
cheese. 

Scale  of  points. — The  following  scale  of  points  is 
in  use  itf  many  places,  the  numbers  indicating  perfect 
quality  in  each  case  and  the  totals  aggregating  100: 

Flavor,  50  Body,  15  Salt,     5 

Texture,  15  Color,  10  Appearance,     5 

In  the  practice  of  many  markets,  salt  is  omitted  and 
appearance  is  given  10  points. 

Method  of  scoring. — The  general  procedure  is  es- 
sentially the  same  as  that  already  described  in  connec- 
tion with  butter  (p.  160). 

Method  of  grading  cheese. — The  same  general  prin- 
ciples apply  as  in  grading  butter  (p.  171).  One  class- 
ification is  into  (i)  "fancy,"  (2)  "firsts,"  and  (3) 
"seconds."  In  the  Canadian  market,  there  are  first, 
second  and  third  grades. 

Score-cards  for  cheese  can  be  prepared  in  a  manner 
similar  to  those  previously  suggested  for  butter  (p.  170) . 

As  in  the  case  of  butter,  the  testing,  scoring  and 
grading  of  cheese  demand  good  judgment  trained  by 
experience.  The  sense  of  smell  and  touch  must  be 
well  developed. 

No  formal  classification  or  grading  of  cheese  is 
made  by  the  New  York  Mercantile  Exchange,  as  is 
done  in  the  case  of  butter. 


CHAPTER    XIV 

Methods   of   Commercial   Testing  and  Scoring 
of  Milk  and  Cream 

In  the  past  few  years,  there  has  been  a  growing 
sentiment  that  some  method  of  testing  the  commer- 
cial value  of  milk  and  cream,  similar  to  that  used  in 
judging  butter  and  cheese,  is  much  needed.  Some 
helpful  work  has  been  done  in  this  direction  by  the 
Dairy  Division  of  the  U.  S.  Department  of  Agricul- 
ture. The  writer  believes  an  efficient  system  will  be 
developed  in  the  near  future,  and,  as  a  basis  for  such 
a  system,  the  present  discussion  is  offered. 

For  convenience  of  treatment,  we  will  classify  milk 
and  cream  according  to  the  purposes  for  which  they 
are  used,  as  follows:  (i)  Market  milk  and  cream, 
when  sold  for  direct  consumption  as  such.  (2)  Cream- 
ery milk  and  cream,,  when  used  for  butter-making. 
(3)  Cheese- factory  milk,  when  used  for  cheese-ma- 
king. (4)  Certified  and  standardized  milk,  when  pro- 
duced under  specific  sanitary  conditions  and  reaching 
a  guaranteed  standard  of  composition. 

TERMS    USED    IN    DESCRIBING    QUALITIES    OF 
MARKET    MILK 

The  qualities  that  are  selected  as  a  basis  in  the  com- 
mercial testing  and  scoring  of  milk  are  the  following: 
(i)  Composition,  (2)  keeping-power,  (3)  flavor,  and, 
we  may  add,  though  of  minor  importance,  (4)  color, 

182 


COMMERCIAL   TESTING    OF    MILK    AND    CREAM      183 

and  (5)  appearance.  For  all  practical  purposes  color 
and  package  can  be  omitted.  In  educational  competi- 
tions they  may  be  included. 

Composition. — By  composition  is  meant  the  per 
cent,  of  fat  and  of  solids-not-fat  in  milk.  The  com- 
position of  milk,  other  things  being  equal,  is  the  direct 
and  only  practicable  measure  of  value,  as  food,  and 
this  must  constitute  an  important  factor  in  judging 
the  value  of  market  milk. 

Testing  composition. — The  percentages  of  fat  and 
of  solids-not-fat  are  found  in  the  manner  described 
on  p.  53  and  p.  137. 

Terms  describing  composition. — Only  two  terms 
need  to  be  used  in  describing  the  composition  of  milk : 
(i)  perfect  and  (2)  defective. 

(1)  Perfect,  as  applied  to  testing  and  scoring  milk, 
means  milk  containing  not  less  than  4  per  cent,  of  fat 
and  not  less  than  9  per  cent,  of  solids-not-fat. 

(2)  Defective   applies   to   milk   containing   less   fat 
or  solids-not-fat  than  required  for  milk  of  "perfect" 
composition. 

The  figures  selected  to  indicate  milk  "perfect"  in 
composition  represent  as  nearly  as  possible  normal 
milk  of  average  composition.  Injustice  would  obvi- 
ously be  done  by  selecting  4.5  or  5  per  cent,  as  the 
amount  of  fat  to  represent  milk  perfect  in  compo- 
sition. It  would,  on  the  other  hand,  be  very  unsatis- 
factory to  take  a  so-called  legal  standard  as  repre- 
senting perfect  composition,  because  it  is  not  a  stand- 
ard at  all  but  simply,  a  method  of  prescribing  the  low- 
est permissible  amounts  of  fat  and  solids  that  will  be 
legally  tolerated  in  milk. 


184  MODERN    METHODS    OF    TESTING    MILK 

Keeping-power  is  an  expression  used  to  indicate 
in  a  general  way  the  length  of  time  milk  remains 
sweet  and  palatable  for  direct  consumption.  In  esti- 
mating the  commercial  value  of  milk,  this  is  an  im- 
portant factor;  since  milk  that  is  sour  or  otherwise 
unpalatable,  or  milk  containing  the  products  of  any 
form  of  undesirable  fermentation,  is  comparatively 
valueless  for  direct  consumption,  however  rich  it  may 
be  in  fat  and  other  solids.  Keeping-power  is  a  matter 
of  much  importance  in  warm  weather,  especially  in 
the  case  of  milk  that  is  transported  long  distances 
before  reaching  the  consumer. 

Testing  keeping-power. — The  keeping-power  of 
milk  is  tested  by  making  determinations  of  (i)  the 
acidity  (p.  96),  (2)  the  dirt  in  suspension  (p.  117), 
(3)  the  fermentation  test  (p.  114),  and  (4)  the  num- 
ber of  bacteria  (when  practicable). 

Terms  describing  keeping-power. — The  terms  used 
in  describing  the  keeping-power  of  milk  are  (i)  per- 
fect, (2)  acidity,  (3)  dirt  in  suspension,  (4)  unde- 
sirable fermentations,  and  (5)  number  of  bacteria  per 
cubic  centimeter. 

(1)  Perfect. — Milk    is    called    perfect    in    keeping- 
power  (a)  when  its  acidity  is  not  above  0.18  per  cent., 
(b)  when  it  contains  no  dirt  in  suspension,  (c)  when 
the  fermentation  test  reveals  nothing  abnormal,  and 
(d)    when   the  number  of  bacteria   does   not   exceed 
100,000  per  cubic  centimeter. 

(2)  Acidity  is  used  to  mean  the  amount  of  appar- 
ent total  acid  calculated  as  lactic,  as   shown  by  the 
amount  of  alkali  neutralized.     For  discussion  of  the 
relation  of  acidity  to  the  temperature  and  cleanliness 
of  milk,  see  pp.  113-114. 


COMMERCIAL   TESTING   OF    MILK   AND   CREAM      185 

(3)  Dirt  in  suspension.     The  amount  of  dirt  sus- 
pended in  milk  may  usually  be  regarded  as  a  rough 
measure  of  the  germ  content  or  cleanliness  of  milk, 
since  the  visible  dirt  we  find  in  milk  is  generally  the 
same  in  source  and  kind. 

(4)  Undesirable  fermentations  refer  to  the  results 
of  the  fermentation  test.     They  may  reveal  themselves 
in    causing   porous,    spongy    curd    and    in    producing 
offensive  odors. 

(5)  Number  of  bacteria  per  cubic  centimeter  is  a 
self-descriptive  term. 

Flavor,  applied  to  milk,  is  used  to  mean  the  odor 
and  taste.  The  abnormal  odors  and  tastes  noticeable 
in  market  milk,  otherwise  good,  come  from  three 
sources :  ( i )  From  certain  things  eaten  by  the  cow, 
as  leeks,  onions,  rag-weed,  cabbage,  etc.  (2)  From 
the  direct  absorption  of  strong-smelling  substances 
present  in  the  air  surrounding  the  milk,  such  as  ma- 
nure, tobacco  smoke,  ensilage,  etc.  (3)  From  stable 
filth  dropping  bodily  into  the  milk. 

Testing  flavor. — This  is  done  by  tasting  and  smell- 
ing the  milk.  The  presence  of  abnormal  odors  can  be 
more  readily  perceived  by  heating  the  milk  for  a  few 
minutes  to  100°  F.  in  a  closed  bottle  or  jar  and  then 
smelling  at  once  on  opening  the  vessel. 

Terms  describing  flavor. — The  following  terms 
may  be  used  in  describing  the  flavor  of  market  milk : 
(i)  Perfect,  (2)  stable  or  cow  manure,  (3)  cowy  or 
animal,  (4)  weedy,  caused  by  leeks,  rag-weed,  etc., 

(5)  vegetable,  such  as  cabbage,  turnip,  ensilage,  etc., 

(6)  bitter,  (7)  fishy,  (8)  sour,  (9)  tainted. 

(i)   Perfect  flavor  in  market  milk  is  indicated  by 


l86  MODERN    METHODS   OF   TESTING    MILK 

freedom  from  all  traces  of  abnormal  odor  and  taste. 
There  should  be  no  marked  odor  and  no  trace  of  any 
offensive  smell.  The  taste  should  be  palatable,  slightly 
saline  and  rich,  without  any  unpalatable  after-taste. 
It  should  not  be  flat  or  insipid. 

The  other  terms  are  mostly  self-descriptive.  Their 
number  could  be  extended  to  cover  more  minute  de- 
tails. The  term  tainted  is  used  to  cover  miscellaneous 
offensive  flavors  not  included  under  other  terms. 

Color  in  relation  to  the  testing  and  scoring  of  mar- 
ket milk  explains  itself.  It  is  in  itself  of  little  prac- 
tical importance  and  may  usually  be  omitted  except  in 
case  of  educational  competitions. 

Testing  color. — The  milk  is  examined  for  color  by 
direct  inspection  in  a  clear  light. 

Terms  describing  color. — In  describing  the  color 
of  market  milk,  the  following  terms  may  be  used : 
(i)  Perfect,  (2)  white,  (3)  bluish,  (4)  high  color, 
(5)  reddish. 

(i)  Perfect  as  applied  to  color  in  milk  indicates  a 
yellowish  color,  not  too  pronounced,  strikingly  differ- 
ent from  the  white  or  bluish  color  of  skim-milk,  but 
not  as  deep  as  the  color  of  cream. 

The  other  terms  explain  themselves.  High  color 
may  be  caused  by  artificial  coloring,  usually  producing 
a  reddish  tint. 

Appearance. — This  term  refers  to  the  appearance 
of  the  can,  bottle  or  other  vessel  containing  the  milk 
and  applies  to  these  in  respect  to  uniformity,  neatness 
and  cleanliness.  This  is  of  relatively  small  practical 
importance  and  may  usually  be  omitted  in  commercial 
work.  It  finds  a  use  in  educational  competitions. 


COMMERCIAL    TESTING   OF    MILK    AND    CREAM      187 

SCORING   MARKET  MILK 

The  qualities  described  above  are  intended  for  use 
in  the  commercial  judging  and  scoring  of  market 
milk.  For  practical  purposes  it  will  be  sufficient  ordi- 
narily to  make  use  of  the  first  three  qualities  men- 
tioned, viz:  (i)  composition,  (2)  keeping-power,  and 
(3)  flavor. 

Scale  of  points. — In  fixing  a  scale  of  points,  we  have 
a  score  of  100  to  distribute  among  the  three  qualities 
last  mentioned.  How  many  points  of  the  100  shall  be 
assigned  to  each?  Here  is  a  chance  for  wide  varia- 
tion of  opinion.  In  actual  experience,  flavor  does  not 
hold  the  same  important  relation  to  market  milk  that 
it  does  to  cheese  and  butter.  A  flavor  that  is  imper- 
ceptible in  the  ordinary  consumption  of  milk  usually 
becomes  concentrated  in  the  process  of  butter-making 
or  cheese-making  and  seriously  affects  the  quality  of 
the  final  product.  A  flavor  must  be  very  bad  to  render 
milk  useless  for  cooking  or  for  purposes  other  than 
direct  drinking.  Hence,  flavor  should  not  receive  so 
high  a  score  in  the  case  of  market  milk  as  in  the  case 
of  butter  or  cheese.  On  the  other  hand,  composition 
should  receive  a  relatively  high  score,  since,  other 
things  being  equal,  it  alone  governs  the  relative  values 
of  different  milks.  The  importance  of  keeping-power 
has  already  been  considered.  For  the  various  reasons 
given,  the  following  scale  of  points  is  suggested  as  a 
desirable  one  for  practical  use : 

Composition 40 

Keeping-power 30 

Flavor 30 


l88  MODERN    METHODS   OF   TESTING    MILK 

The  numbers  indicate  perfect  quality  in  each  case 
and  the  totals  aggregate  100.  The  numbers  assigned 
could  be  varied  considerably  and  still  give  equally 
satisfactory  results  in  practise. 

Method  of  scoring. — The  milk  is  examined  in  the 
manner  previously  described  and  defects  are  indicated 
by  making  deductions  from  the  perfect  score  in  the 
following  manner: 

(1)  Composition. — The  perfect  score  of  40  points 
is  reduced  one  point  for  each  o.i  per  cent,  below  4  per 
cent,  of  fat  and  one  point  for  each  o.i  per  cent,  below 
9  per  cent,  of  solids-not-fat. 

(2)  Keeping-power. — The   perfect   score   of   30   is 
to  be  reduced  (a)  one  point  for  each  o.oi  per  cent,  of 
acidity  above  0.18;   (b)   a  certain  number  of  points, 
according  to  the  judgment  of  the  examiner,  for  dirt 
in  suspension;  (c)  a  certain  number  of  points  for  any 
abnormal  results  shown  by  the  fermentation  test;  and 
(d)  one  point  for  each  100,000  bacteria  above  100,000 
in  I  cubic  centimeter  of  milk,  when  this  determination 
is  made. 

(3)  Flavor. — The  perfect  score  of  30  is  reduced  by 
the  presence  of  abnormal  odors  or  tastes,  the  examiner 
using  his  judgment  as  to  the  amount  of  reduction. 

JUDGING  MILK   FOR   MANUFACTURE   OF 
BUTTER   AND    CHEESE 

For  milk  that  is  to  be  used  for  butter-making  or 
cheese-making,  a  somewhat  different  method  is  sug- 
gested for  judging  and  scoring.  Since  such  milk  is 
or  should  be  paid  for  on  the  basis  of  the  fat,  the  sys- 


COMMERCIAL   TESTING   OF    MILK   AND   CREAM      189 

tem  of  judging  and  scoring  should  be  such  as  to  affect 
the  value  or  the  amount  of  the  fat  for  which  payment 
is  received.  Such  a  method  is  given  in  the  following 
statements : 

(1)  Score  the  milk  directly  for  two  qualities  only, 
(a)    keeping-power  and   (b)   flavor.     For  perfection, 
allow  50  points  for  keeping-power  and  50  points  for 
flavor. 

(2)  From  the  total  amount   (pounds)   of  fat  con- 
tained in  the  milk  furnished  by  each  patron,  deduct, 
according  to  the  results  of  scoring,  a  certain  amount 
of  fat,  which  is  found  by  multiplying  the  total  amount 
of  fat  in  the  milk  by  0.25  per  cent,  and  this  result  by 
the  number  of  points  scored  below  100. 

(3)  Use  the  number  of  pounds  of  fat  thus  found 
as  the  actual  amount  of  fat  on  which  to  base  dividends. 
To  illustrate,  a  patron  furnishes  1,000  pounds  of  milk, 
containing  4  per  cent,  of  fat,  which  scores  90  in  keep- 
ing-power and  flavor.    What  deduction  shall  be  made 
from  the  fat  for  the  score  of  90?    The  amount  (1,000 
pounds)  of  milk  furnished  contains  40  pounds  of  fat. 
This  number  (40)  multiplied  by  0.25  per  cent.'  (Rule 
i,  p.  193)  equals  o.i  pound  of  fat,  which  multiplied  by 
10,  the  number  of  points  scored  below   100,  equals  i 
pound.     The  total  amount  (40  pounds)  of  fat,  dimin- 
ished by  the  subtraction  of  i,  leaves  39  pounds,  which 
amount  would  be  used  as  a  basis  in  making  this  pa- 
tron's dividend. 

The  judging  of  flavor  and  keeping-power  is  carried 
out  as  previously  described  for  market  milk.  In 
cheese-making,  it  is  important  to  make  full  use  of  the 
fermentation  test  (p.  114). 


I9O  MODERN    METHODS   OF   TESTING    MILK 

COMMERCIAL  TESTING  AND   SCORING  OF  CER- 
TIFIED AND   STANDARDIZED   MILK 

Certified  milk  usually  guarantees  (i)  the  per  cent, 
of  fat,  (2)  the  per  cent,  of  total  solids  or  solids-not- 
fat,  and  (3)  bacteria  below  a  specified  number.  Stand- 
ardized milk  usually  guarantees  only  the  per  cent,  of 
fat. 

The  examination  and  scoring  of  certified  or  of  stand- 
ardized milk  are  conducted  in  the  same  manner  as  in 
the  case  of  market  milk,  except  that  the  scoring  is 
based  upon  the  guarantees,  so  far  as  these  are  given. 
The  guaranteed  per  cent,  of  fat  and  of  solids-not-fat 
and  the  number  of  bacteria  are  to  be  taken  as  repre- 
senting the  perfect  score  in  place  of  the  figures  given 
above  for  market  milk,  and  deductions  from  the  per- 
fect score  for  defects  are  made  on  the  basis  of  the 
guarantees.  For  example,  if  a  certified  milk  is  guar- 
anteed to  contain  5  per  cent,  of  fat,  then,  in  order  to 
score  40  in  composition,  the  milk  must  contain  5  per 
cent,  of  fat  and,  in  case  of  any  shortage,  a  proportion- 
ate deduction  should  be  made  from  the  perfect  score 
of  40. 

COMMERCIAL    TESTING    AND    SCORING^    OF 
CREAM 

Market  cream  is  that  which  is  sold  for  direct  con- 
sumption. The  method  of  examining  and  scoring 
market  cream  is  essentially  the  same  as  in  the  case 
of  market  milk.  In  composition,  cream  is  not  exam- 
ined or  scored  for  solids  but  for  fat  only.  Another 
quality  might  be  added  in  case  of  cream,  that  of  body, 


COMMERCIAL    TESTING   OF    MILK    AND    CREAM      IQI 

by  which  is  meant  the  consistency  of  the  cream,  espe- 
cially with  reference  to  the  presence  or  absence  of 
lumps,  complete  evenness  of  consistency  being  required 
for  perfection  of  body. 

In  composition,  not  less  than  20  per  cent,  of  fat 
should  be  used  as  a  basis  for  perfection  and  from  the 
perfect  score  of  40  is  deducted  one  point  for  each  0.5 
per  cent,  of  fat  below  20.  Acidity  and  flavor  are  of 
special  importance  in  market  cream.  The  acidity 
should  not  be  allowed  to  be  above  0.2  per  cent,  for 
perfect  cream. 

Creamery  cream  is  that  which  is  intended  for  but- 
ter-making. The  same  general  procedure  is  employed 
as  in  the  case  of  milk  that  is  to  be  used  for  butter- 
making,  which,  adapted  to  cream,  is  as  follows : 

(1)  Score  the  cream  directly  for  two  qualities  only, 
(a)    keeping-power  and    (b)    flavor.     For  perfection 
allow  50  points  for  each  quality. 

(2)  From  the  total  amount   (pounds)   of  fat  con- 
tained in  the  cream  furnished  by  each  patron  deduct, 
according  to  the  results  of  scoring,  a  certain  amount 
of  fat,  which  is  found  by  multiplying  the  total  amount 
of  fat  in  the  cream  by  0.25  per  cent,  and  this  result 
by  the  number  of  points  scored  below  100. 

(3)  Use  the  number  of  pounds  of  fat  thus  found  as 
a  basis  for  making  dividends. 

To  illustrate,  a  patron  furnishes  500  pounds  of 
cream,  containing  20  per  cent,  of  fat,  which  scores  90 
in  keeping-power  and  flavor.  What  deduction  shall 
be  made  from  the  fat  for  the  score  of  90  ?  The  amount 
(500  pounds)  of  cream  furnished  contains  100  pounds 
of  fat.  This  number  (100)  multiplied  by  0.25  per 


192  MODERN    METHODS    OF    TESTING    MILK 

cent.  (Rule  i,  p.  193)  equals  0.25  pound  of  fat,  which 
multiplied  by  10,  the  number  of  points  scored  below 
100,  equals  2.5  pounds.  The  total  amount  (100  pounds) 
of  fat,  diminished  by  the  subtraction  of  2.5,  leaves 
97.5  pounds  of  fat,  which  amount  would  be  used  as  a 
basis  in  making  this  patron's  dividend. 


CHAPTER   XV 

Arithmetic  of  Milk  and  Milk  Products 

In  connection  with  the  testing  of  milk  and  milk 
products,  especially  in  some  of  the  practical  applica- 
tions, various  arithmetical  calculations  are  often  nec- 
essary. Special  attention  may  need  to  be  given  to  the 
methods  employed  in  solving  such  problems  as  are 
presented,  and  a  few  pages  are  here  devoted  to  the 
treatment  of  some  of  the  more  common  problems  in 
a  systematic,  comprehensive  form,  convenient  for  ready 
reference.  In  creameries,  cheese-factories,  etc.,  where 
much  arithmetical  work  is  involved  in  making  divi- 
dends, saving  of  time  is  effected  by  using  calculations 
or  tables,  which  are  published  in  book  form. 

I.  FINDING  WEIGHT  OF  ANY  CONSTITUENT 

Rule. — To  find  the  weight  of  any  constituent  in  milk 
or  milk  products,  when  the  weight  of  the  milk  or  its 
product  and  the  per  cent,  of  the  constituent  are  known, 
multiply  the  weight  by  the  number  indicating  the  per 
cent,  of  the  constituent  and  divide  the  result  by  100. 
Example:  How  many  pounds  of  fat  in  675  pounds 
of  milk  testing  4.6  per  cent,  of  fat?  6?5iX4-6  =  31.05, 
the  number  of  pounds  of  fat. 


193 


194  MODERN    METHODS   OF   TESTING   MILK 

EXAMPLES  FOR  PRACTICE 

(1)  How  many  pounds  of  fat  in  2,000  pounds  of 
cheese  containing  35  per  cent,  of  fat? 

(2)  How  much  water  in   1,000  pounds  of  butter 
containing  14.5  per  cent,  of  water? 

(3)  How  many  grams  of  milk-sugar  are  there  in 
500  grams  of  milk  containing  5   per  cent,   of  milk- 
sugar? 

(4)  How   much   fat   is   there   in    1,200  pounds   of 
cream  testing  44  per  cent,  of  fat? 

(5)  How  much  fat  is  there  in  5,000  pounds  of  skim- 
milk  testing  .15  per  cent,  of  fat? 


2.  FINDING  PER   CENT.   OF  ANY   CONSTITUENT 

Rule. — To  find  the  per  cent,  of  any  constituent  in 
milk,  etc.,  when  the  weight  of  the  milk,  etc.,  and  the 
weight  of  the  constituent  are  known,  multiply  the 
weight  of  the  constituent  by  100  and  divide  the-  result 
by  the  weight  of  the  milk,  etc.  Example:  What  is 
the  per  cent,  of  fat  in  675  pounds  of  milk  containing 
31.05  pounds  of  fat?  31'°|*IO°  =  4-6  per  cent. 

EXAMPLES  FOR  PRACTICE 

(1)  What  is  the  per  cent,  of  fat  in  120  pounds  of 
butter  containing  96  pounds  of  fat? 

(2)  What  is  the  per  cent,  of  water  in  600  pounds 
of  cheese  containing  210  pounds  of  water? 


ARITHMETIC   OF    MILK   AND   MILK   PRODUCTS      195 

3.  FINDING  PER  CENT.  OF  SOLIDS  IN  MILK 

Rule. — To  find  the  per  cent,  of  solids  in  milk  when 
the  Quevenne  lactometer  reading  and  the  per  cent. 
of  fat  are  known,  divide  the  lactometer  reading  by  4, 
and  to  the  result  add  the  per  cent,  of  fat  multiplied  by 
1.2.  (See  p.  137.) 

4.    FINDING    PER    CENT.    OF    SOLIDS-NOT-FAT 
IN  MILK 

Rule. — To  find  the  per  cent,  of  solids-not-fat  in 
milk  when  the  Quevenne  lactometer  reading  and  the 
per  cent,  of  fat  are  known,  divide  the  lactometer  read- 
ing by  4,  and  to  the  result  add  the  per  cent,  of  fat 
multiplied  by  .2.  (See  p.  137.) 

EXAMPLES  FOR  PRACTICE  UNDER  RULES 
3  AND  4 

(1)  What  is  the  per  cent,  of  solids  in  milk  testing 
4  per  cent,  of  fat  and  showing  a  lactometer  reading 
of  32? 

(2)  What  is  the  per  cent,  of  solids-not-fat  in  the 
same  milk  as  in   (i)  ? 

(3)  What  is  the  per  cent,  (a)  of  solids  and  (b)  of 
solids-not-fat  in  a  milk  testing  2.5   per  cent,   of  fat 
and  showing  a  lactometer  reading  of  27? 

(4)  What  is  the  per  cent,  (a)  of  solids  and  (b)  of 
solids-not-fat  in  milk  testing  .2  per  cent,  of  fat  and 
showing  a  lactometer  reading  of  36? 


196  MODERN    METHODS   OF   TESTING   MILK 

5.  FINDING  THE  "OVERRUN"  IN  BUTTER- 
MAKING 

The  weight  of  butter  produced  is  greater  than  the 
amount  of  fat  in  the  milk  or  cream  from  which  the 
butter  is  obtained,  because  butter,  in  addition  to  its 
fat,  contains  water,  salt  and  curd.  Such  excess  is 
called  the  "overrun"  and  may  be  readily  ascertained 
by  finding  the  yield  of  butter  for  one  pound  of  fat. 
While  some  milk-fat  is  lost  in  the  skim-milk  and  but- 
termilk and  in  handling  during  butter-making,  enough 
water,  salt  and  curd  are  added  to  the  fat  to  make  up 
these  losses  and  something  more.  The  amount  of  but- 
ter yield  for  a  pound  of  fat  in  milk  or  cream  neces- 
sarily varies  with  the  variation  of  losses  of  fat  in  skim- 
milk  and  in  butter-making  and  the  amount  of  water, 
salt,  etc.,  retained  in  the  butter.  Hence  the  "overrun" 
varies.  When  the  operations  of  skimming  milk  and 
butter-making  are  properly  managed,  one  pound  of 
fat  in  milk  produces  about  1.17  (about  I  1-6)  pounds 
of  butter.  Hence,  the  "overrun"  is  .17  or  one-sixth, 
(17  per  cent).  The  "overrun"  in  case  of  cream  aver- 
ages about  .03  higher  than  in  case  of  milk,  according 
to  Hills. 

Rule. — To  find  the  "overrun"  when  the  weight 
of  butter  made  from  a  given  amount  of  milk  or  cream 
and  the  per  cent,  of  fat  in  the  milk  or  cream  are  known, 
•find  the  number  of  pounds  of  fat  in  the  milk  or  cream 
by  Rule  i,  and  divide  the  weight  of  butter  by  the  weight 
of  fat.  From  the  result  subtract  i.  Example:  What 
is  the  "overrun"  in  case  of  milk  testing  4  per  cent,  of 


ARITHMETIC   OF    MILK  AND    MILK   PRODUCTS       197 

fat,  when  we  make  135  pounds  of  butter  from  3,000 
pounds  of  milk?  Applying  Rule  i,  3°°^4  =120,  pounds 
of  fat  in  milk;  and  135^-120=1.125  (il/%)  pounds. 
1.125 — I=-I25  (I2-5  Per  cent.)  or  */£.  Therefore,  the 
"overrun"  is  .125  or  ^  pound,  that  is,  for  each  pound 
of  fat  in  milk  there  will  be  made  iy$  pounds  of  butter. 

6.  FINDING  THE  YIELD  OF  BUTTER 

Rule. — To  find  the  yield  of  butter  when  the  per 
cent,  of  fat  in  milk  and  the  weight  of  milk  are  known, 
find  the  number  of  pounds  of  fat  in  milk  by  Rule  i 
and  multiply  this  result  by  1.17  or  i  1-6.  Example: 
How  much  butter  is  made  from  1,000  pounds  of  milk 
containing  4  per  cent,  of  fat?  Applying  Rule  I, 

—  =  40,   pounds   of   fat   in   milk;   and   40x1.17= 


46.8,  pounds  of  butter  yield. 

In  the  case  of  cream  apply  the  foregoing  rule,  ex- 
cept to  multiply  by  1.20  instead  of  1.17. 

The  application  of  this  rule  finds  use  in  checking 
creamery  work.  If  the  yield,  in  case  of  milk,  is  not 
in  proportion  to  an  "overrun"  of  15  to  17  per  cent, 
and  in  case  of  cream,  20  per  cent.,  one  should  ascer- 
tain why  and  then  correct  such  faults  as  are  found  to 
exist  in  the  form  of  losses  of  fat  or  retaining  too  little 
water.  When  the  proportion  of  butter  to  fat  greatly 
exceeds  1.17  in  the  case  of  milk,  too  much  water  is 
retained  in  the  butter,  or  else  the  fat-test  is  improperly 
made  or  the  results  purposely  read  too  low. 


198  MODERN    METHODS   OF   TESTING    MILK 

EXAMPLES  FOR  PRACTICE  UNDER  RULES 
5  AND  6 

(1)  How  much  butter  should  be  made  from  5,000 
pounds  of  milk  testing  5  per  cent,  of  fat? 

(2)  What  is  the  "overrun"  when  4,000  pounds  of 
milk,  testing  4  per  cent,  of  fat,  yield  180  pounds  of 
butter? 

(3)  A  butter-maker  has  10,000  pounds  of  milk,  test- 
ing 4  per  cent,  of  fat;  in  skimming  this,  he  produces 
8,000  pounds  of  skim-milk,  testing  .15   per  'cent,   of 
fat.     After  churning,  he  has  1,600  pounds  of  butter- 
milk testing  .2  per  cent,  of  fat.     The  loss  of  fat  in 
handling  the  cream  and  making  the  butter  amounts  to 
4  pounds,    (a)   How  much  fat  is  left  in  the  butter? 

(b)  How  many  pounds  of  butter  should  be  made? 

(c)  What  is  the  "overrun"  if  he  produces  450  pounds 
of  butter? 

(4)  How  much  butter  should  be  made  from  1,000 
pounds  of  cream  testing  35  per  cent,  of  fat? 

7.  FINDING  YIELD   OF   CHEESE   FOR   MILK-FAT 

Rule. — To  find  the  yield  of  green  cheese  for  a  pound 
of  fat  in  milk  when  the  weight  of  the  cheese  made 
from  a  given  amount  of  milk  and  the  per  cent,  of  fat 
in  milk  are  known,  find  the  number  of  pounds  of  fat 
in  milk  by  Rule  i,  and  divide  the  weight  of  cheese  by 
the  weight  of  fat.  Example:  How  much  cheese  is 
made  for  one  pound  of  fat  in  milk,  testing  4  per  cent, 
of  fat,  when  we  make  63  pounds  of  cheese  from  600 
pounds  of  milk?  Applying  Rule  I,  6o0^4  =  24 
pounds  of  fat  in  milk;  63^-24=2.67  pounds  of  cheese 


ARITHMETIC   OF    MILK   AND    MILK    PRODUCTS       199 

made  for  one  pound  of  fat  in  milk.  In  connection  with 
cheese,  this  is  the  same  kind  of  relation  as  the  "over- 
run" in  butter.  In  cheese-making  a  pound  of  fat 
in  milk  has  added  to  it  enough  casein,  water,  salt, 
etc.,  to  increase  the  weight  from  I  of  fat  to  2.7  (more 
or  less)  pounds  of  cheese. 

8.  FINDING  YIELD  OF  CHEESE  FROM  FAT  IN 
MILK 

Rule. — To  find  the  yield  of  green  cheese  from  100 
pounds  of  milk  when  the  per  cent,  of  fat  in  milk  is 
known,  multiply  the  per  cent,  of  fat  in  milk  by  2.7.  Ex- 
ample: How  much  cheese  should  be  made  from  100 
pounds  of  milk  testing  3.7  per  cent,  of  fat?  3.7x2.7= 
9.99  pounds. 

This  rule  applies  only  to  normal  milk  containing 
3.6  to  3.8  per  cent  of  fat.  For  milk  containing  fat 
above  3.8  per  cent.,  the  results  are  usually  too  high; 
and  for  milks  containing  less  than  3.6  per  cent,  of 
fat,  the  results  are  usually  too  low. 

9.  FINDING  YIELD   OF  CHEESE  FROM  FAT  AND 
CASEIN  IN  MILK 

Rule. — To  find  the  yield  of  green  cheese  from  100 
pounds  of  milk  when  the  per  cent,  of  fat  and  of  casein 
in  milk  is  known,  multiply  the  per  cent,  of  casein  by 
2.5  and  to  this  result  add  the  per  cent,  of  fat  multiplied 
by  i.i.  Example :  How  much  cheese  can  be  made 
from  loo  pounds  of  milk  containing  4  per  cent,  of 
fat  and  2.6  per  cent,  of  casein?  (2.6x2.5) +(4x1.1)  = 
10.90  pounds  of  green  cheese. 


2OO  MODERN    METHODS   OF   TESTING   MILK 

10.  FINDING  PER  CENT.  OF  CASEIN  IN  MILK 
FROM  FAT 

Rule. — To  find  the  per  cent,  of  casein  in  milk  when 
the  per  cent,  of  fat  is  known,  subtract  3  from  the  per 
cent  of  fat  in  milk,  multiply  the  result  by  .4  and  add 
this  result  to  2.1.  Example:  How  much  casein  is  there 
in  milk  containing  4.5  per  cent,  of  fat?  (4.5 — 3)x.4+ 
2.1=2.70  per  cent  of  casein. 

This  rule  is  based  upon  the  writer's  work,  showing 
that  milk  testing  3  per  cent  of  fat  contains  an  average 
of  about  2.1  per  cent  of  casein,  and  that  the  casein  in- 
creases, on  an  average,  .4  per  cent,  when  the  per  cent, 
of  milk  increases  I  per  cent,  above  3.  This  is  especially 
true  of  milks  ranging  from  3  to  4.5  per  cent,  of  fat 
when  the  milk  is  produced  at  the  same  stage  of  lacta- 
tion. In  the  later  stages  of  lactation  the  ratio  of  ca- 
sein to  fat  is  greater  than  is  indicated  by  this  rule. 
(See  p.  12.) 

In  applying  Rule  9,  Rule  10  can  be  used  to  find 
the  per  cent,  of  casein  in  milk  when  only  the  per  cent, 
of  fat  is  known.  For  example,  how  much  cheese  can 
be  made  from  100  pounds  of  milk  containing  4.25  per 
cent,  of  fat?  By  Rule  10,  (4.25 — 3)x.4+2.i=2.6,  the 
per  cent,  of  casein  in  the  milk.  Then  by  Rule  9,  (2.6 
x2.5)+(4.25xi.i)  =  ii.i8  pounds. 

The  above  rule  can  be  used  in  finding  the  amount 
of  casein  and  albumin  together,  the  factor  2.9  being 
added  instead  of  2.1. 


ARITHMETIC  OF   MILK  AND   MILK   PRODUCTS      2OI 

11.  FINDING  YIELD  OF  CHEESE  FROM  FAT  AND 
LACTOMETER 

Rule. — To  find  how  much  green  cheese  can  be  made 
from  100  pounds  of  milk  when  the  per  cent,  of  fat  in 
milk  and  the  lactometer  reading  are  known,  find  the 
per  cent,  of  solids-not-fat  by  Rule  4,  divide  the  re- 
sult by  3  and  to  this  add  the  per  cent,  of  fat  multiplied 
by  .91,  and  finally  multiply  the  result  by  1.58. 

This  rule  was  devised  by  Dr.  Babcock  and  gives 
good  results.  It  may  be  expressed  also  in  the  follow- 
ing form:  (•*"«»•-»<*•**  +  fat  x  .91)  X  1.58. 

EXAMPLES  FOR  PRACTICE  UNDER  RULES 
8  TO  11 

1 i )  What  is  the  per  cent,  of  casein  in  milk  contain- 
ing (a)  3-50,  (b)  3-6o,  (c)  4,  (d)  44  per  cent,  of  fat? 

(2)  How  much  green  cheese  should  be  made  from 
loo  pounds  of  the  different  milks  mentioned  in  the 
preceding  example?  (Apply  Rule  9  and  Rule  10). 

(3)  How  much  green  cheese  should  be  made  from 
18,000  pounds  of  milk  testing  3.75  per  cent,  of  fat? 

(4)  How  much  green  cheese  should  be  made  from 
loo  pounds  of  milk  testing  4  per  cent,  of  fat  and  show- 
ing a  lactometer  reading  of  33? 

(5)  What  is  the  per  cent,  of  casein  and  albumin  in 
milk  containing  (a)   3.50,   (b)   3.80,   (c)   4.30,   (d)    5 
per  cent,  of  fat? 

12.  FINDING   DIVIDENDS    ON   FAT   BASIS   AT 
CREAMERIES 

Rule. — To  calculate  the  amount  of  each  patron's 
dividend  at  creameries  on  the  basis  of  the  fat  in  the 
milk,  multiply  the  amount  of  the  milk-fat  delivered  by 
each  patron  by  the  price  of  one  pound  of  fat. 


2O2  MODERN    METHODS  OF  TESTING   MILK 

This  rule  can  be  made  more  clear  by  considering 
the  process  in  three  separate  steps,  assuming  that  the 
creamery  is  operated  on  the  co-operative  plan. 

Step  i.  By  Rule  I  find  the  amount  of  milk- fat  fur- 
nished by  each  patron  during  the  dividend  period. 

Step  2.  Find  the  net  value  of  one  pound  of  milk- 
fat  by  dividing  the  total  net  receipts  by  the  total  num- 
ber of  pounds  of  fat  delivered  by  all  the  patrons  during 
the  dividend  period. 

Step  3.  Multiply  the  number  of  pounds  of  fat  de- 
livered by  each  patron  by  the  net  price  received  for 
one  pound  of  fat. 

Example :  Step  i .  The  data  and  results  are  indicated 
in  tabular  form  as  follows: 


Pounds  of  Milk 

Per  cent. 

Pounds  of 

NAME  OF 

delivered  during 

of/at 

fat  in  milk 

PATRON 

dividend  period 

in  milk 

delivered 

A           . 

...      350 

X 

4.0 

I4.OO 

B 

.       .       .      650 

X 

3-6 

2340 

C           . 

...      835 

X 

5-2 

43-42 

D           . 

...      965 

X 

44 

42.46 

E 

.  I,2OO 

X 

4.2 

50.40 

Total 

number  of  pounds 

of 

fat  delivered  by 



171.68 

Step  2.  From  the  amount  of  fat  indicated  above, 
the  amount  of  butter  made  was  195  pounds,  which 
realized  18  cents  a  pound  after  deducting  all  expenses, 
making  a  total  of  $35.10.  This  sum  divided  by  173.68, 
the  total  pounds  of  fat  delivered,  gives  20.2  cents  as 
the  net  price  received  for  each  pound  of  fat. 


ARITHMETIC   OF    MILK   AND    MILK   PRODUCTS      2O3 

Step  3.  The  data  and  results  are  indicated  in  tabu- 
lar form,  as  follows: 

Pounds  Net  price  Amount  of 

NAME  OF  of  fat  received  for  fat  dividend  due 

PATRON  delivered  per  pound  each  patron 

A  .  .  14.00  x  20.2  cents      =  $2.83 

B  .  .  23.40  x  =  473 

C  .  .  43-42  X  -                                =  8.77 

D  .  .  42.46  x  =  8.58 

E  .  .  50.40  x  =  10.18 

When  both  milk  and  cream  are  used  in  a  creamery, 
the  pounds  of  fat  delivered  in  the  form  of  cream  are 
found  by  applying  Step  I  above  and  then  multiplying 
the  result  by  1.02.  From  this  point  on,  the  process  of 
calculating  dividends  is  the  same  as  above  described. 

13.  FINDING  DIVIDENDS  ON  FAT  BASIS  AT 
CHEESE-FACTORIES 

Rule. — To  calculate  the  amount  of  each  patron's 
dividend  at  cheese-factories  on  the  basis  of  the  fat  in 
the  milk,  proceed  as  under  Rule  12. 

14.  FINDING  AMOUNTS  OF  MILK,  ETC.,  TO  USE 
IN  MODIFYING  NORMAL  MILK 

The  practice  of  modifying  or  standardizing  milk 
for  special  market  purposes  is  constantly  increasing. 
This  consists  in  increasing  or  decreasing  the  per  cent, 
of  fat  in  a  normal  milk.  The  per  cent,  of  fat  in  a 
normal  milk  may  be  increased  (i)  by  adding  cream, 
(2)  by  adding  milk  richer  in  fat,  or  (3)  by  skimming 
part  of  the  normal  milk  with  a  separator  and  then  put- 
ting the  cream  thus  obtained  back  into  the  rest  of  the 
normal  milk.  The  per  cent,  of  fat  in  a  normal  milk 


204  MODERN    METHODS  OF  TESTING   MILK 

may  be  decreased  without  adding  water,  (i)  by  add- 
ing skim-milk,  (2)  by  adding  milk  poorer  in  fat,  or 
(3)  by  skimming  part  of  the  milk  and  then  putting 
the  skim-milk  thus  obtained  back  into  the  rest  of  the 
normal  milk. 

Prof.  R.  A.  Pearson,  of  Cornell  University,  has  de- 
vised an  ingenious  method  by  which  one  can  accu- 
rately, quickly  and  easily  find  the  amounts  of  milk, 
cream  and  skim-milk  to  be  used  in  modifying  or  stand- 
ardizing milk  in  order  to  produce  a  milk  containing  a 
desired  per  cent,  of  milk-fat.  The  following  diagram 
and  explanation  may  serve  to  make  clearer  the  work- 
ing of  the  method: 


Per  cent,  fat  in  milk=A—  -         -  ,C—  B  or  B—  C  (pounds  of  A  to  use 


Per  cent,  fat  inj 

cream,  etc.         |  =C .A— B  or  B— A  (pounds  of  C  to  use) 

Cream  or  skim- 
milk,  etc. 

Let  A  represent  the  per  cent,  of  fat  in  the  milk 
to  be  modified. 

Let  B  represent  the  per  cent,  of  fat  desired  in  the 
modified  milk. 

Let  C  represent  the  per  cent,  of  fat  in  the  milk, 
cream  or  skim-milk  which  is  to  be  used  in  increasing 
or  decreasing  the  per  cent,  of  fat. 

The  problem  is  to  find  in  what  proportions  we  shall 
use  the  milk,  etc.,  containing  A  and  C,  in  order  to  ob- 
tain a  product  containing  B. 

When  the  per  cent,  of  fat  in  the  normal  milk  is 
to  be  increased,  A  is  less  than  B,  while  C  is  greater 
than  B.  In  this  case,  B  minus  A  gives  the  pounds  of 


ARITHMETIC   OF    MILK   AND    MILK    PRODUCTS       205 

the  product  containing  C  to  be  used,  while  C  minus  B 
gives  the  pounds  of  milk  (A)  to  be  used  or,  expressed 
in  another  way,  the  procedure  becomes,  B — Ai=pounds 
of  product  containing  C  to  be  used,  and  C — B=pounds 
of  milk  (A)  to  use. 

When  the  per  cent,  of  fat  in  the  normal  milk  is 
to  be  decreased  in  the  modified  milk,  the  procedure  is 
thus  indicated:  A — B— pounds  of  product  containing 
C  to  be  used  and  B — C— pounds  of  milk  (A)  to  be 
used. 

The  simplicity  of  the  method  becomes  readily  ap- 
parent when  practically  illustrated. 

(i)  When  the  per  cent,  of  fat  in  milk  is  to  be  in- 
creased by  addition  of  cream  or  richer  milk.  Rule. — 
From  the  per  cent,  of  fat  desired  in  the  modified  milk 
subtract  the  per  cent,  of  fat  in  the  milk  to  be  modified, 
and  the  result  is  the  number  of  pounds  of  cream  or 
richer  milk  to  be  used.  From  the  per  cent,  of  fat  in 
the  cream  or  richer  milk  subtract  the  per  cent,  of  fat 
desired  in  the  modified  milk,  and  the  result  is  the  num- 
ber of  pounds  to  use  of  the  milk  to  be  modified.  Ex- 
ample: What  relative  amounts  of  normal  milk  and 
cream  must  be  used  to  produce  milk  containing  4.5 
(B)  per  cent,  of  fat,  when  the  normal  milk  contains 
3.5  (A)  per  cent,  of  fat  and  the  cream  25  (C)  per 
cent.  ? 

A=3.s MllH. c— B=2o.5  (pounds  of  milk  to  use). 

B=4-5 

C=25 B — A=i  (pounds  of  cream  to  use). 

Cream 

The  results  mean  that  20.5  pounds  of  milk  contain- 
ing 3.5  per  cent,  of  fat,  mixed  with  I  pound  of  cream 
containing  25  per  cent,  of  fat,  will  produce  a  modified 


2O6  MODERN    METHODS   OF  TESTING   MILK 

milk  containing  4.5  per  cent,  of  fat.  If,  in  place  of 
cream,  a  milk  containing  more  than  3.5  per  cent,  of 
fat  were  used,  the  process  would  be  the  same. 

(a)  If  it  is  desired  to  know  how  much  such  cream 
must  be  used  in  standardizing  1,000  pounds  of  such 
milk,  divide   1,000  by  20.5   (C  —  B)   and  multiply  by 
I  (B  —  A,)  which  will  give  48.8  pounds  of  cream  to  be 
added  and  1048.8  pounds  of  the  modified  milk. 

(b)  If  it  is  desired  to  know  how  much  such  cream 
and  milk  to  use  to  make  1,000  pounds  of  the  modified 
milk,  divide  1,000  by  21.5   (C  —  B)  +  (B  —  A),  which 
is  46.5,  and  multiply  this  amount  by  20.5  (C  —  B)  and 
by  I    (B  —  A),  which  will  give  953.5   pounds  of  3.5 
per  cent,  milk  and  46.5  pounds  of  25  per  cent,  cream. 

(2)  When  the  per  cent,  of  fat  in  milk  is  to  be  in- 
creased by  removing  a  portion  of  the  milk-serum 
(skim-milk).  Rule.  —  From  the  per  cent,  of  fat  de- 
sired in  the  modified  milk  subtract  the  per  cent,  of  fat 
in  the  milk  to  be  modified,  and  the  result  is  the  number 
of  pounds  of  skim-milk  to  be  removed.  The  per  cent. 
of  fat  in  the  modified  milk  is  the  number  of  pounds  to 
use  of  the  milk  to  be  modified.  This  is  done  by  sep- 
arating the  cream  from  a  portion  of  the  milk  and  then 
adding  it  to  the  normal  milk.  The  skim-milk  can  be 
assumed  to  contain  practically  no  fat.  Example  :  How 
much  skim-milk  should  be  removed  from  milk  con- 
taining 3.9  per  cent,  of  fat,  in  order  to  produce  a  mod- 
ified milk  containing  5  per  cent,  of  fat? 


A==3.9 


C=o.o 


B=5 


Skim-milk 


B-C=5  (pounds  of  milk  to  use). 


B — A=i  i  (pounds  of  skim-milk  to  remove). 


ARITHMETIC   OF    MILK   AND    MILK    PRODUCTS      2O7 

In  this  case  we  add  nothing,  so  that  C  equals  o  and 
B  —  C=5  —  0=5.  The  results  mean  that  for  5  pounds 
of  the  milk,  we  should  remove  i.i  pounds  of  skim- 
milk,  thus  reducing  5  pounds  of  milk  containing  3.9 
per  cent,  of  fat  to  3.9  pounds  of  modified  milk  contain- 
ing 5  per  cent,  of  fat. 

Applying  these  results  to  a  specific  case,  how  much 
skim-milk  should  be  removed  from  980  pounds  of 
3.9  per  cent,  milk  to  increase  the  fat  to  5  per  cent? 
Divide  980  by  5  (B  —  C),  which  gives  196,  and  mul- 
tiply this  by  i.i  (B  —  A)  which  gives  215.6  pounds  of 
milk-serum  or  skim-milk  to  be  removed,  leaving  764.4 
pounds  of  modified  5  per  cent.  milk. 

(3)  When  the  per  cent,  of  fat  is  to  be  decreased  by 
adding  skim-milk.  Rule  —  From  the  per  cent,  of  fat 
in  the  milk  to  be  modified  subtract  the  per  cent,  of  fat 
desired  in  the  modified  milk,  and  the  result  is  the  num- 
ber of  pounds  of  skim-milk  to  be  used.  From  the  per 
cent,  of  fat  desired  in  the  modified  milk,  subtract  the 
per  cent,  of  fat  in  the  skim-milk,  and  the  result  is  the 
number  of  pounds  to  use  of  the  milk  to  be  modified. 
Example:  How  much  skim-milk  containing  .1  per 
cent  of  fat  should  be  added  to  milk  containing  5  per 
cent,  of  fat  to  reduce  the  fat  to  3.9  per  cent.? 


A==5 


C=.i 


B=3-9 


Skim-milk 


B—  C=3.8  (pounds  of  5  per  cent.  milk). 


A — B=I.I  (pounds  of  skim-milk). 


(a)  How  much  skim-milk  should  be  added  to  1,000 
pounds  of  5  per  cent,  milk  to  produce  3.9  per  cent, 
milk?  Divide  1,000  by  3.8,  giving  263,  and  multiply 
the  result  by  i.i,  which  gives  289,  the  number  of 


2O8  MODERN    METHODS   OF  TESTING   MILK 

pounds  of  skim-milk.     There  would  be  1,289  pounds 
of  3.9  per  cent.  milk. 

(b)  How  much  skim-milk  is  needed  to  produce 
1,000  pounds  of  modified  3.9  per  cent,  milk?  Divide 
i  ,000  by  4.9,  which  gives  204.08.  This,  multiplied  by 
3.8,  gives  775.5  pounds  of  5  per  cent,  milk  to  use  and, 
multiplied  by  i.i,  gives  224.5  pounds  of  skim-milk. 

EXAMPLES  FOR  PRACTICE 

(1)  What  amount  of  milk  containing  4.7  per  cent, 
of  fat,  and  of  cream  containing  30  per  cent,  of  fat, 
should  be  mixed  in  order  to  produce  740  pounds  of 
milk  containing  6  per  cent,  of  fat? 

(2)  Mix  milk  containing  5.2  per  cent,  of  fat  with 
milk  containing  3.3  per  cent  of  fat  in  such  amounts 
as  to  produce  950  pounds  of  milk  containing  4.1  per 
cent,  of  fat. 

(3)  How  many  pounds  of  separator  skim-milk  must 
be  mixed  with   100  pounds   of   cream   containing  20 
per  cent,  of  fat  in  order  to  produce  a  modified  milk 
containing  5  per  cent,  of  fat? 

(4)  How  many  pounds  of  skim-milk  must  be  mixed 
with  two  pounds  of  4.5  per  cent,  milk  in  order  to  pro- 
duce a  mixture  containing  3  per  cent,  of  fat? 

(5)  How  much  skim-milk  must  be  removed  from 
milk  containing  3  per  cent,  of  fat  in  order  to  increase 
the  fat  to  3.7  per  cent.? 

15.   CORRECTING   QUEVENNE   LACTOMETER 
READING  FOR  TEMPERATURE 

Rule. — For  each  degree  F.  above  60°  F.  add  .1,  and 
for  each  degree  below  60°  F.  subtract  .1  (See  p.  131). 


ARITHMETIC   OF    MILK   AND    MILK    PRODUC1S      209 

16.     CONVERTING  QUEVENNE  INTO   BOARD   OF 
HEALTH   LACTOMETER  DEGREES 

Rule. — Divide  the  Quevenne  reading  by  .29.  (See 
P-  1340 

17.  CONVERTING  BOARD   OF  HEALTH   INTO 
QUEVENNE  LACTOMETER  DEGREES 

Rule. — Multiply  the  Board  of  Health  reading  by 
.29.  (See  p.  134.) 

18.    CORRECTING  BOARD  OF  HEALTH  LACTOM- 
ETER READING  FOR  TEMPERATURE 

Rule. — For  each  degree  F.  of  temperature  above 
60°  F.  add  .3,  and  for  each  degree  below  60°  F.  sub- 
tract .3.  (Seep.  136.) 

19.  CHANGING  VOLUME  INTO  WEIGHT 

Rule. — To  convert  a  known  volume  of  a  liquid 
into  pounds  when  the  specific  gravity  is  known,  mul- 
tiply the  specific  gravity  of  the  liquid  by  the  weight 
of  an  equal  volume  of  water.  Example :  One  gallon  of 
water  weighs  8.33  pounds;  what  is  the  weight  of  a 
gallon  of  milk  whose  specific  gravity  is  1.032?  Mul- 
tiplying 8.33  by  1,032,  we  have  as  the  answer  8.6 
pounds. 

20.  CHANGING  POUNDS  OF  MILK  INTO  QUARTS 

Rule. — Divide  the  number  of  pounds  of  milk  by  2.15. 
Example:  How  many  quarts  of  milk  in  100  pounds? 
46.5  quarts. 


210  MODERN    METHODS   OF   TESTING   MILK 

21.  CHANGING  QUARTS  OF  MILK  INTO  POUNDS 

Rule.  —  Multiply  the  number  of  quarts  by  2.15.  Ex- 
ample: How  many  pounds  in  40  quarts  of  milk?  40 
X2.  1  5=86  pounds. 

22.  CHANGING  DEGREES  FAHRENHEIT  INTO 
DEGREES  CENTIGRADE 

Rule.  —  From    the  degrees  F.  subtract  32  and  mul- 
tiply the  result  by  5-9.    Example:   162°  F.=z(i62  —  32) 
2°  C 


23.  CHANGING  DEGREES  CENTIGRADE  INTO 
DEGREES  FAHRENHEIT 

Rule.  —  Multiply  the  degrees  C.  by  9-5  and  add  32. 
Example:  72°  C.=  (  72x9-5  )+32=  162°  F. 


24.  FINDING  THE  TRUE  AVERAGE 

Rule. — To  find  the  true  average  per  cent,  of  fat  in 
different  lots  of  milk  or  milk  products,  find  the  weight 
of  fat  in  each  separate  lot  by  Rule  i,  add  these  amounts 
and  divide  the  sum  by  the  total  weight  of  milk  or  milk 
products.  Example:  What  is  the  average  per  cent, 
of  fat  in  the  following  lots  of  milk? 

Pounds  Per  cent.  Pounds 

of  milk  of  fat  of  fat 

400  containing  4.3 17.2 

300  34 i°-2 

800  5-2 41.0 

100  3.1 3-1 

1, 600  72-1 


ARITHMETIC   OF    MILK   AND    MILK   PRODUCTS      211 

Applying  Rule  i,  we  find  the  weight  of  fat  in  each 
lot  of  milk,  the  results  being  indicated  in  the  third 
column  above.  The  total  amount  of  fat  in  all  of  the 
milks  is  72.1  pounds,  which,  divided  by  1,600  (the 
total  weight  of  milk),  gives  4.5  as  the  real  average 
per  cent,  of  fat  in  all  the  milk. 

It  is  wrong  to  regard  as  the  average  per  cent,  the 
result  obtained  by  adding  the  per  cents,  directly  and 
then  dividing  this  sum  by  the  number  of  lots  repre- 
sented, unless  the  amounts  of  milk  or  milk  products 
are  equal.  Thus,  in  the  foregoing  example,  the  result 
of  such  a  wrong  method  would  make  the  average  4 
per  cent.,  when  it  is  really  4.5. 

The  same  principle  explains  why  we  do  not  get  a 
true  average  composite  sample,  when  we  take  the 
same  amount  of  milk  from  different  lots  that  vary 
considerably  in  weight  and  per  cent,  of  fat. 

EXAMPLES  FOR  PRACTICE 

1 i )  Find  the  average  per  cent,  of  fat  in  the  follow- 
ing lots  of  milk:     1,200  pounds,  3  per  cent,  of  fat; 
2,000  pounds,  5  per  cent,  of  fat ;  6,000  pounds,  4  per 
cent,  of  fat;  and  1,800  pounds,  3.5  per  cent,  of  fat. 

(2)  Find   the   average   per   cent,   of   fat   in    1,000 
pounds  of  cream,  40  per  cent,  of  fat;  1,600  pounds,  30 
per  cent,  of  fat;  and  400  pounds,  20  per  cent,  of  fat. 

25.    FINDING  AMOUNT  OF  CREAM 

Rule. — To  find  the  amount  of  cream  produced  for 
loo  pounds  of  milk  when  the  per  cent,  of  fat  in  milk 
and  in  cream  is  known,  divide  the  per  cent,  of  fat  in 


212  MODERN    METHODS   OF   TESTING   MILK 

milk  by  the  per  cent,  of  fat  in  cream  and  multiply  the 
result  by  100.  Example :  How  many  pounds  of 
cream  containing  25  per  cent,  of  fat  are  produced 
from  100, pounds  of  milk  containing  5  per  cent,  of  fat? 
5-r-25=.2.  .2x100=20,  number  of  pounds  of  cream 
with  25  per  cent,  of  fat. 

26.    FINDING  AMOUNT  OF  SKIM-MILK 

Rule. — To  find  the  amount  of  skim-milk  for  100 
pounds  of  milk  when  the  per  cent,  of  fat  in  milk  and 
in  cream  is  known,  find  the  amount  of  cream  by  Rule 
25  and  then  subtract  this  from  100.  Example :  How 
much  skim-milk  is  produced  from  100  pounds  of  milk 
containing  4  per  cent,  of  fat  when  the  cream  contains 
25  per  cent  of  fat?  4-^25=.  16;  .16x100=16;  100 — 
16=84,  number  of  pounds  of  skim-milk. 

27.    FINDING  AMOUNT  OF  BUTTERMILK 

Rule. — To  find  the  amount  of  buttermilk  for  100 
pounds  of  milk  when  the  per  cent,  of  fat  in  milk  and 
in  cream  is  known,  multiply  the  amount  of  fat  in  100 
pounds  of  milk  by  1.17  and  subtract  the  result  from 
the  amount  of  cream.  Example:  How  many  pounds 
of  buttermilk  are  produced  for  100  pounds  of  milk 
containing  4  per  cent,  of  fat,  when  the  cream  used 
contains  25  per  cent,  of  fat?  4x1.17=4.68  (pounds 
of  butter  made)  ;  4-^-25x100=16  (pounds  of  25  per 
cent,  cream)  ;  16 — 4.68=11.32  (pounds  of  buttermilk). 


ARITHMETIC   OF    MILK   AND   MILK    PRODUCTS      213 

28.     FINDING  SPECIFIC  GRAVITY  OF 
MILK-SOLIDS 

Rule. — To  find  the  specific  gravity  of  milk-solids, 
when  the  specific  gravity  of  the  milk  and  per  cent,  of 
milk-solids  are  known,  multiply  the  specific  gravity  of 
the  milk  by  100,  from  the  result  subtract  100  and  di- 
vide this  result  by  the  specific  gravity  of  the  milk.  Sub- 
tract the  last  result  from  the  per  cent,  of  milk-solids 
and  then  divide  this  result  by  the  per  cent,  of  milk- 
solids.  (See  p.  139.) 

29.    FINDING  AMOUNT  OF  ADDED  WATER 

IN  MILK 
See  page  142. 

30.  FINDING  AMOUNT  OF  MOISTURE  IN  BUTTER 

Rule. — To  find  the  approximate  amount  of  mois- 
ture in  butter,  add  j  to  the  per  cent,  of  fat  (obtained 
by  the  method  described  on  p.  85)  and  subtract  the 
sum  from  100.  In  adding  3,  allowance  is  made  for 
i  per  cent,  of  casein  and  2  per  cent,  of  salt  in  the 
butter.  The  results  by  this  method  should  in  most 
cases  be  within  I  or  2  per  cent,  of  the  correct  fig- 
ures. Example:  How  much  moisture  in  butter  con- 
taining 83.7  per  cent,  of  fat?  83.7+3=86.7;  100 — 86.7 
=  13.3,  the  per  cent,  of  moisture. 

31.  TABLE    SHOWING    APPROXIMATE    EQUIVA- 

LENTS OF  METRIC  SYSTEM 

fluid  ounce  =  29.60  cubic  centimeters    (cc.) 

quart  =      0.95  liter   (1.) 

gallon  =      3.8     liters. 

grain  =  65.         miligrams    (mg.) 

ounce   (av.)  =  28.35  grams  (gm.) 

pound  =        .45  kilogram   (kg.) 


INDEX 


PAGE 

Acid,  lactic,   from  milk-sugar  .   .  13 

Estimation  of 96-108 

Acid,    sulphuric,   action   in    Bab- 
cock  test 33 

Adding   to    milk 56 

Care    in    handling 44 

Effect     of     strong     and     weak 

acid 42 

Measuring    for   test 56 

Mixing  with  milk 58 

Strength    of 42 

Temperature    when   used   ...  57 

Testing  strength  of 43 

Acid-hydrometer 43 

Acid-measures 36,  37 

Testing  accuracy  of     49 

Acid    solution     98 

Acid  tester 43 

Acid  tests,    Mann's 101 

Spillman's     I  ....  105 

Acids,  action  on  alkalis 97 

In  milk-fat 3 

Volatile    acids 4 

Acidity,  indicators  for 98 

In  milk,   causes  and  kinds  of  96 

In  milk  in  relation  to  bacteria  113 

In  rich  and  poor  cream  ....  110 

Principles  of  testing 97 

Rapid  estimation  of 106 

Testing  of,   in  cheese 110 

In  cream  and  milk  .  .  .  101-108 

In    whey 109 

Acidometer 43 

Adulterations  of  butter 149 

Cheese     150 

Cream 148 

Milk  .                                             .  141 


PAGE 

Age  of  composite  samples  when 

tested 31 

Of  milk,  testing  by  rennet  .  .  126 

Albumin  in  milk 11 

In   relation  to  casein   .....  12 

Alkalis,  action  on  acids 97 

Alkali  test,   Purdue 107 

Alkaline  solution   .  .  .  . 98 

Alkaline-tablet  test 103 

Analysis.     See  Composition. 

Annatto,  detection  of,  in   milk  .  147 

Apparatus  in   Babcock  test   ...  34 

Testing  accuracy  of 45 

Appearance  in  judging  and  scor- 
ing  butter 167 

Cheese     180 

Arithmetic  of  milk  and  products 

193-212 

Ash   in   milk 13 

Average,  true,  how  to  find    ...  210 

Babcock  test 32 

Acid   measure 36 

Acid  used  in 42 

Action  of  acid 33 

Apparatus      34 

Benefits  of  use 32 

Bottles 34,,  70,  82 

Centrifugal   machines   ....  38-40 

For  butter    . 85 

For  buttermilk 83 

For   cheese 83 

For  condensed  milk 91 

For  cream 69 

For    milk 53 

For  milk  powder  ........  94 

For  skim-milk 81 

215 


2l6 


MODERN    METHODS   OF   TESTING    MILK 


PAGE 

Babcock  test  for  whey 81 

Modifications   of 66 

Operation  of 53 

Pipette     35 

Principles  underlying 33 

Reading    results 61 

Testers 38 

Testing  accuracy  of  apparatus     45 
Use  of  centrifugal  force  ...     33 

Water  used  in 60 

Bacteria  and  acidity  of  milk  .  .  113 
Bacterial  condition  of  milk,  test- 
ing      113 

Bichromate  of  potash  as  preser- 
vative           29 

Board  of  Health  lactometer  ...  133 

Body  of  butter 162 

Of    cheese     176 

Borax  in  milk,  detection  of  ...   148 
Bottles,  Babcock  test,  for  cream 

70,  71 

For  milk 34 

For  skim-milk,  whey,  etc.    .  .     82 
Butter,  appearance  in  judging  .   167 

Body  of 162 

Calculating  dividends  for  ...  201 

Calculating  water  in 213 

Classes   of 170 

Color    of 164 

Commercial    testing,    judging, 

and  scoring 158 

Composition  of 16 

Definition   of 18 

Finish   of 167 

Flavor  of 159 

Grades  of 171 

Gray's  test  for  water  in  ....     86 

Judging 158 

Moisture   in 86,    163 

"Overrun,"    how    to    calculate  196 

Package 167 

Qualities   of 159 

Renovated 18,  149 

Salt   in 166 


PAGE 

Butter,  sampling  for  fat-test  .  .     85 
For  judging  and  scoring  .  .  158 

Scale  of  points 168 

Score-cards 168 

Scoring 167 

Standard   of 18 

Texture   of 161 

Yield  of,  how  to  calculate    .  .   197 
Butter-fat.     See  Milk-fat. 
Buttermilk,   composition  of  ...     16 

Testing   fat   in 83 

Yield   of,    calculating 212 

Butter-trier 159 

Butyrometer,  Gerber's 67 

By-products  of  milk,  composition 

of 16 

Calcium   casein 9 

Calibration  of  glassware 45 

Casein   in   milk,   action   of   acids 

on       9 

Of  alkalis 10 

Of  heat 10 

Of  rennet 10 

Calculating   amount    of,    from 

fat  in  milk 200 

Composition  of 9 

Lactate 10 

Per  cent,  in  milk 12 

Products   formed   from    ....  11 

Proportion  to  albumin    ....  12 
Centigrade     degrees     calculating 

to  Fahrenheit 210 

Centrifugal     force     in     Babcock 

test 33 

Machines 38 

Centrifuges 38,   40,  118 

Cheddar  cheese,  American,  com- 
position of 16 

Commercial    testing,    judging, 

and    scoring 173,  181 

Cheese,  adulterations  of 150 

Appearance  and  finish  of  ...  180 

Body  of     176 


INDEX 


2I7 


PAGE 

Cheese,     calculating     yield     of, 

from   fat 198 

From  fat  and  casein    ....  199 

Classes  of 181 

Color  of 178 

Commercial    judging,    testing, 

and   scoring  of     173 

Commercial  qualities  of  ....   173 

Composition   of      16 

Definition   of 19 

Dividends  from,  calculating    .  203 

Finish   of 180 

Flavor  of 173 

Judging   of 173 

Package 180 

Salt   in 179 

Sampling  for  fat-testing  ....     84 
For  judging  and   scoring      .   173 

Score-cards 181 

Scoring 181 

Standard 19 

Testing  acidity  in 110 

Testing  commercial  qualities  .   173 

Testing  fat   in 83 

Texture 175 

Trier    for    sampling 173 

Yield   of,  calculating 198 

Cheese-factory,    calculating  divi- 
dends  of 203 

Chemistry  of  cow's  milk    ....        1 
Churned  samples  of  milk  ....     21 

Prevention    of 22 

Sampling     of 21 

Cleaning  greasy  glassware  ....     49 
Collecting   sediment   in   milk.   .   .   117 
Coloring   matter   in   milk,    detec- 
tion    of 147 

Commercial  testing,  judging,  and 

scoring   of   butter 158 

Of  certified  milk 190 

Of    cheese 173 

Of  cream 190 

Of  milk 187 

Of  standardized  milk.  .  .190 


PAGE 

Composite  samples,  age  for  test- 
ing          31 

Care  of 30 

Description 24 

Method  of  taking 26 

Preserving 28 

Sampling   for   test 54 

Sample-jars 25 

Composition  of  butter 16 

Buttermilk 16 

Casein 9 

Composition  of  cheese 16 

Milk 15 

Milk-fat 3 

Skim-milk     16 

Whey 16 

Condensed  milk,  testing  fat  of.  .     91 
Corrosive  sublimate  as  preserva- 
tive         28 

Cows,  testing  on  farm 151 

Cows'  milk,  analyses  of 15 

Chemistry  of 1 

Composition  of 15 

Definition  of 16 

Standard  of 17 

Cream,  acidity  of,  testing  .  .  96,  112 

Adulterations  of 148 

Bottles,  bulb-necked 70 

Straight-necked 71 

Calculating  yield  of 211 

Color  of  fat-column 64 

Commercial     testing,     scorinj 

and  judging 190 

Definition    of 18 

Keeping  samples  of 73 

Method  of  sampling 72 

Poor  and   rich,   acidity  in    .  .  110 
Preparing  sample  for  testing  .     73 

Standard '.  .  .     18 

Testing   fat  in 69-76 

Weighing   sample   of 75 

Cream   scales 72 

Creamery   dividends,   calculation 

of 201 

Curd-test,    Wisconsin     .  .   114 


2l8 


MODERN    METHODS   OF   TESTING    MILK 


PAGE 

Cylinder,   for  lactometer    ....  133 
Spillman's,  acid-test  .  .....  105 

Definitions    of     milk    and    milk 

products 16-19 

Detection  in  milk,  of  annatto  .  .  147 

Borax 148 

Coloring   matter 147 

Formalin 147 

Of  skimmed  milk    ....  144,   146 

Of  watered  milk 141,   146 

Dipper,  sampling 27 

Dirt  in  milk,  testing 117 

Dividends,  calculating,  at  cream- 
eries    , 201 

At    cheese-factories 203 

Double-necked  test-bottles  ....     82 
Draining-rack      51 

Farm,  testing  milk  on  ......  151 

Farrington's    alkaline-tablet    test  103 

Bottle-cleaner 51,  52 

Fat  in  milk.     See  milk-fat. 

Fat-column,  black  particles  in     .  64 

Gas-bubbles  in 65 

Measuring,  in  cream-testing    .  77 

White  particles  in 65 

Fat-globules,   in  milk,   number   .  4 

Size 4 

Influences  affecting 5 

In  cheese,  etc 5 

Fermentation  test  of  milk,  Wis- 
consin       114 

Gerber's      117 

Finish   of  butter 167 

Of  cheese 180 

Flavor  of  butter 159 

Cheese     173 

Milk,   cream,  etc 185 

Formalin    in    milk,    as   preserva- 
tive   .  29 

Detection   of 147 

Frozen  milk,  sampling  of  ....  23 

Galactase  in  milk 11 

Gerber's    butyrometer 67 

Fermentation   test 117 


PAGE 

Gerber's  "Sal"  test 68 

Glassware  in  Babcock  test,   cali- 
bration   of 45 

Cleaning  of 49 

Testing  accuracy  of     45 

Globulin   in   milk 11 

Glycerin   in   milk-fat 3 

Grades  of  butter 171 

Of  cheese 181 

Gray's  test   for   water   in   butter  86 

Greiner's  automatic  pipette   ...  36 

Hand-testers 39,  118 

Hydrometer    for   testing    specific 

gravity 130 

Testing  strength  of  acid    ...  43 

Infant  foods,  testing  fat  in    .  .     93 
Indicator  in  testing  acidity  ...     98 

Jars,    waste,   for   emptying   test- 
bottles 50 

Jars,  for  composite  samples  ...     25 

Judging  butter 158-167 

Cheese 173-181 

Cream      190 

Milk     182-190 

Kumiss,   definition   of 19 

Lactate,   casein 10 

Lactate  acid  in  milk 13,  96 

Estimation  of 96-108 

From  milk  sugar  ........     13 

Lactose     13 

Lactometer,  application   .  .  .   127-140 

Board  of  Health 133 

Bi-chromate,  effect  on  .  .  .  .  .  136 

Cylinder    for 133 

Method  of  using 131 

Quevenne      130 

Temperature,  effect  on   .   129,    131 

Mann's  acid  test 101 

Marschall   rennet   test 123 

Measures  for  acid 36 

Measuring,  acid     56 

Fat-column  in  testing  cream   .  77 

In  testing  milk 63 


INDEX 


219 


PAGE 

Metric   system,   equivalents   of   .  213 

Milk,   acidity   of 96 

Adding  acid  to     56 

Adulteration    of 141 

Age  of,  testing 126 

Albumin  in 11 

Analyses  of 15 

Arithmetic   of 193 

Ash    in 13 

Chemistry  of 1 

Churned,  sampling  of 21 

Color   of 186 

Certified,  judging 190 

Composite  sampling  of    ....     24 

Composition  of 15 

Condensed      17,   91 

Definition  of 16 

Detection   of   adulterations   in  141 

Flavor  of 185 

Frozen,  sampling  of 23 

Gases  in 14 

Judging  and  scoring 187 

Keeping  power  of 184 

Mixing  with  acid 58 

Modified,  to  prepare     203 

Nitrogen,   compounds  of    ...       8 

Salts  in 13 

Sampling    of 20-31 

Sampling  with  pipette 54 

Scale  of  points  in  judging    .  .   187 

Scoring  of 187 

Skimmed,   detection    of    .  144,  146 

Sour,   sampling  of 23 

Souring   of 13 

Specific  gravity  of 127 

Standard  of     17 

Standardized,  to  prepare    .  .  .  203 
Standardized,       judging      and 

scoring 190 

Temperature  for  testing  ....     57 
Terms    used    in    judging    and 

scoring 182 

Testing  acidity   of 96-108 

Total  solids  of 3,  137 

Watered,  detection  of     .  .141,   146 
Milk-albumin 11 


PAGE 

Milk-bottle,  use  of  in  cream-test- 
ing          69 

Milk,  Casein.     See  Casein. 
Milk-fat,  color  of  in  Babcock  test     64 

Composition  of 3. 

Definition    of 18 

Glycerin  in 4 

Influenced    by    various    condi- 
tions       5-8 

In  relation  to  butter  yield  .  .   197 

In   relation  to   Casein 200 

In  relation  to  cheese 198 

Method  of  testing,  in  butter  .     85 

In   buttermilk 83 

In  cheese     83 

In  condensed  milk 91 

In  cream  ..........  69-77 

In   milk     53-66 

In    milk   powders 94 

In  skim-milk 81 

In  whey 83 

Per  cent,   in  foremilk  ...          8 

In  strippings     8 

Standard   of 18 

Variation  of,  in  milk  ....       5 

Volatile  acids  in 4 

Milk-globulin 11 

Milk,  measuring  with  pipette  .  .  54 
Milk  powders,  testing  of  ....  94 
Milk  products,  arithmetic  of  .  .  193 

Composition  of 16 

Judging   and    scoring   .   .  .   158-192 

Milk  serum 15 

Milk-solids,   composition   of   .   .  3,    14 
Estimating  by  lactometer  .  .  .   137 

Specific  gravity  of 139 

Milk-sugar 13 

Milk  testing,  Babcock  test  .  .  32,  53 

On  the  farm 151 

Mixing  milk  and  acid 58 

Moisture.     See  water. 

Monrad  rennet-test 121 

Neutral  solutions 98 

Neutralization     97 


22O 


MODERN    METHODS   OF  TESTING    MILK 


PAGE 

Nitrogen   compounds  of   milk   .  .     8 

In  relation  to  fat 12,  144 

New  York  Board  of  Health  lac- 
tometer   133 

Oleomargarin,   test  for 149 

"Overrun"    in    butter,    how    to 

find 196 

Package,  judging  and  scoring  of, 

in  butter 167 

In  cheese 180 

Per  cent,  of  any  constituent  of 
milk   and   products,   how   to 

find 194 

Percentages,     average,     how     to 

find 210 

Phenolphthalein  as  indicator   .  .     98 

Pipette,  in  Babcock  test 35 

Accuracy  of,  testing 49 

Correct  way  to  use    ......     55 

Greiner's 36 

In  cream  testing 75 

Sampling  milk  with 54 

Wagner's 36 

Potassium-bichromate 29 

Pounds,  to  change  to  quarts  .  .  209 
Powdered  milk,  testing  of  ....     94 
Preservatives  for  composite  sam- 
ples         28 

Detection  of,  in  milk 147 

Purdue  alkali  test 107 

Qualities,  commercial,  of  butter  159 

Cheese     173 

Milk      182 

Cream 190 

Quarts  to  change  to  pounds  .  .  210 
Quevenne     lactometer,     descrip- 
tion  of 130 

Correcting  for  temperature  .  .  131 

How.  to  use 131 

Compared      with      Board      of 
Health  lactometer 135 

Rack,  draining  for  test -bottles  .     51 

For  composite   samples   ....     26 

Rennet-test,  Marschall's 123 


PAGE 

Rennet-test,  Monrad's 121 

Renovated  butter,  definition  of  .  18 

How  to  detect 149 

Standard    of 19 

Richmond's    slide-rule    for    find- 
ing milk-solids 138 

Russian  test  for  fat  in  milk  and 

products 66 

"Sal"  test  for  fat  in  milk,  etc., 

Gerber's 68 

Salt  in  butter,  commercial  judg- 
ing and  scoring 166 

In  cheese 179 

Salts  in  milk 13 

Samples.    See  Composite  samples. 

Sampling  butter 85,    158 

Cheese 83,  173 

Cream     72 

Milk,    composite 24 

Frozen 23 

Partially  churned 21 

Partially  creamed 20 

Sour     23 

With  pipette 54 

Sampling-dipper     27 

Sampling-tubes 27 

Scales      for      weighing      cheese, 

cream,   etc 72 

Score-cards  for  butter 168 

Cheese     181 

Scoring   butter 167 

Cheese     181 

Cream 190 

Milk      187 

Standardized  milk 190 

Sediment    in    milk,    how   to    test 

for 117 

Serum  of  milk 15 

Solids  of 15 

Sinacid  test  for  fat  in  milk,  etc.     67, 
Skim-milk,  composition  of  ....     16 

Detection   of 144,    146 

How  to  calculate  yield  of     .  .  212 

Test-bottles 82 

Testing  for  fat  in 81 


INDEX 


221 


PAGE 

Slide-rule,    Richmond's    for    cal- 
culating  solids      138 

Sodium    carbonate    in    milk,    de- 
tection  of 148 

Solids-not-fat   in  milk 15 

How  to  find  amount  of  ....  137 

Solids,  total,  in  milk.     See  Milk- 
solids. 

Sour  milk,  cause  of 13 

Sampling    of 23 

Specific  gravity  of  milk 127 

Cylinder     133 

Effect  of  fat  on 128 

Effect  of  temperature  on  ...   129 

Effect  of  water  on     128 

How  to   find 129 

Specific  gravity,  of  milk  solids  .  139 
Table  for  temperature  correc- 
tion     132 

Speed  of  testers 40 

Spillman's  acid-test  cylinder    .  .  105 

Standard  of  butter 18 

Butter-fat      18 

Cheese     19 

Condensed   milk 17 

Cream      18 

Milk-fat 18 

Standard  of  Renovated  butter  .     19 
Skim-milk      17 

Steam-turbine  tester 38 

Sugar   of   milk 13 

Sulphuric  acid.     See  acid. 

Sweetened  condensed  milk  ...     17 

Table    of    correction    of    specific 

gTavity   for   temperatures     .  132 
Equivalents  of  metric  systems  213 
Of      degrees     of      Board      of 
Health    and    Quevenne    lac- 
tometers      135 

Temperature   of   acid   in  testing 

milk      57 

Of  fat-column  when  read  ...  62 
In  relation  to  specific  gravity  129 
Of  milk  when  tested 57 


PAGE 

Terms      describing      commercial 

qualities   of  butter 159 

Of    cheese     173 

Of  cream  and  milk 182 

Test,  Babcock.   See  Babcock  Test. 

Curd,  Wisconsin  .  . 114 

Fermentation,   Gerber's   ....  117 

Rennet,  Marschall 123 

Monrad 121 

"Sal,"    Gerber's 68 

Russian 66 

Sinacid       67 

Test-bottles,  accuracy  of,  testing  45 

Bulb-necked,  cream 70 

Calibration 45 

Cleaning     49 

Cream 70 

Double-necked 79 

Drain-rack 51 

Test,    Milk 34 

Rinser 50 

Skim-milk      82 

Straight-necked  cream 71 

Tester      46 

Whirling 59 

Testers,   Babcock 37 

Bottle 46 

Electrical 40 

Estimating  speed  of 40 

Hand 39 

Steam-turbine     38 

Testing,  accuracy  of  test  bottles, 

etc 45 

Acidity,  of  cream,  milk,  etc.  96-108 

Age  of  milk 126 

Butter      85 

Cheese     83 

Condensed  milk 91 

Cows  on  farm 151 

Dirt  in  milk 117 

Infant   foods   93 

Milk  powders '.  .  94 

Pepsin      125 

Rennet     121 

Texture,  commercial,  of  butter  .  161 


222 


MODERN    METHODS   OF   TESTING    MILK 


PAGE 

Texture,  commercial,  of  cheese  .  175 

Titration     100 

Total  solids  of  milk.     See  milk- 
solids. 

Trier  for  testing  butter 159 

Cheese     173 

Tube,    sampling      ...  * 27 

Turbine   testers      38 

Volatile  acids  in  milk-fat  .  .  .  >.       4 
Volume    of    liquid,    changing    to 

weight 209 

Wagner's  pipette 36 

Skim-milk  bottle 82 

Waste  acid  jar 50 

Water,   in  milk,  amount  of  ...        1 

Causes  of  variation 2 

Detection  of,  in  adulterated    .  141 
In  butter,  calculation  of    ...  213 

In  butter-testing 86 

In     commercial     testing     and 

judging  of  butter 163 

In  milk  and  milk  products   15,  16 


PAGE 

Water  used  in  Babcock  test  ...     60 
Watered  milk,  detection  of  ...   141 
Weighing  samples  of  cream  ...     75 
Weight    of    any    constituent    of 
milk   and   products,    how   to 

find 193 

Changing  to  volume 209 

Weights    and    measures,    equiva- 
lents of  metric   system  ...  213 

Wheyj    composition    of 16 

Definition   of 19 

Testing  of 81 

Whirling  test-bottles 59 

Wisconsin  curd-test 114 

Yield   of  butter,  how  to  calculate  197 

Buttermilk 212 

Cheese,    for   fat 198 

Cheese,  from  fat 199 

Cheese,  from  fat  and  casein  .  199 
Cheese,    from    fat    and    lacto- 
meter        201 

Cream      211 

Skim-milk  .  212 


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PROFITABLE    DAIRYING 

A  Practical  Guide  to  Successful  Dairy  Management.    By  C.  L.  PECK 

The  introductory  chapter  of  this  book  consists  of  a  minute  description  of  the 
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Never  perhaps  has  the  description  of  any  farm  caused  a  more  profound  sensa- 
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The  author  of  this  volume  is  a  well  known,  practical  dairyman,  who  has 
made  dairying  a  marked  success,  and  who,  in  this  volume,  gives  such  practical 
hints  on  dairying  as  will  enable  the  reader  to  improve  his  methods,  better  his 
conditions  and  more  clearly  attain  that  point  in  business  known  as  success. 
The  treatment  of  the  entire  subject  is  thoroughly  practical  in  every  detail, 
being  principally  a  description  of  the  methods  practiced  by  the  author,  and 
which  after  a  lifetime  of  experience  and  study  he  has  found  most  advantage- 
ous. Yet  the  scientific  bearing  on  the  subject  has  not  been  neglected,  as  the 
author  has  availed  himself  of  all  the  most  recent  discoveries  and  advance- 
ments in  science,  thus  making  the  work  authoritative,  practically  as  well  as 
scientifically. 

Separate  chapters  are  devoted  to  the  importance  of  the  dairy,  physiology, 
and  secretion  of  milk,  future  of  dairying,  dairy  breeds,  selection  of  a  breed, 
the  dairy  cow  and  the  dairy  sire,  dairy  standard,  care  and  feed  of  the  dairy 
cow,  care  of  the  calf,  milking,  when  to  have  cows  come  fresh,  feeds  and  their 
value,  care  of  the  milk,  device  for  ripening  cream,  churning,  marketing  dairy 
butter,  the  dairy  barn,  silo  and  silage,  miscellaneous  topics,  necessary  appli- 
ances, general  hints,  dairy  remedies. 

Illustrated.      5x7  inches.      174   Pages.      Cloth.      Price,   75  cents 


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The  Cereals  in  America 

By  THOMAS  F.  HUNT,  M.S.,  D.  Agr.  If  you  raise  five 
acres  of  any  kind  of  grain  you  cannot  afford  to  be  without  this 
book.  It  is  in  every  way  the  best  book  on  the  subject  that  has 
ever  been  written.  It  treats  of  the  cultivation  and  improve- 
ment of  every  grain  crop  raised  in  America  in  a  thoroughly 
practical  and  accurate  manner.  The  subject  matter  includes  a 
comprehensive  and  succinct  treatise  of  wheat,  maize,  oats, 
barley,  rye,  rice,  sorghum  (kafir  corn),  and  buckwheat,  as 
related  particularly  to  American  conditions.  Fiijt-hand  knowl- 
edge has  been  the  policy  of  the  author  in  his  work,  and  every 
crop  treated  is  presented  in  the  light  of  individual  study  of 
the  plant.  If  you  have  this  book  you  have  the  latest  and  best 
that  has  been  written  upon  the  subject.  Illustrated.  450  pages. 
51-2x8  inches.  Cloth $1.75 

The  Potato 

By  SAMUEL  FRAZER.  A  reliable  guide  on  the  cultivation  of 
the  potato,  its  development,  manuring  and  fertilizing,  planting, 
tillage,  sprays  and  spraying,  breeding  new  varieties,  harvesting, 
storing,  marketing,  etc.,  etc.  Taken  all  in  all  it  is  the  most 
complete,  reliable  and  authoritative  work  on  the  potato  ever 
published  in  America.  Illustrated.  200  pages.  5x7  inches. 
Cloth $0.75 


Farm  Grasses  of  the  United  States  of  America 

By  WILLIAM  JASPER  SPILLMAN.  A  practical  treatise  on 
the  grass  crop,  seeding  and  management  of  meadows  and 
pastures,  description  of  the  best  varieties,  the  seed  and  its 
impurities,  grasses  for  special  conditions,  lawns  and  lawn 
grasses,  etc.,  etc.  In  preparing  this  volume  the  author's  object 
has  been  to  present,  in  connected  form,  the  main  facts  con- 
cerning the  grasses  grown  on  American  farms.  Every  phase 
of  the  subject  is  viewed  from  the  farmer's  standpoint.  Illus- 
trated. 248  pages.  5x7  inches.  Cloth.  .  .  .  $1.00 

The  Book  of  Corn 

By  HERBERT  MYRICK,  assisted  by  A.  D.  SHAMEL,  E.  A. 
BURNETT,  ALBERT  W.  FULTON,  B.  W.  SNOW,  and  other  most 
capable  specialists.  A  complete  treatise  on  the  culture, 
marketing  and  uses  of  maize  in  America  and  elsewhere,  for 
farmers,  dealers  and  others.  Illustrated.  372  pages.  5x7 
inches.  Cloth.  .  .  .  .  • $1.50 

The    Hop  —  Its    Culture  and  Care,  Marketing 
and  Manufacture 

By  HERBERT  MYRICK.  A  practical  handbook  on  the  most 
approved  methods  in  growing,  harvesting,  curing  and  selling 
hops,  and  on  the  use  and  manufacture  of  hops.  The  result  of 
years  of  research  and  observation,  it  is  a  volume  destined  to  be 
an  authority  on  this  crop  for  many  years  to  come.  It  takes  up 
every  detail  from  preparing  the  soil  and  laying  out  the  yard, 
to  curing  and  selling  the  crop.  Every  line  represents  the 
ripest  judgment  and  experience  of  experts.  Size,  5x8;  pages, 
300;  illustrations,  nearly  150;  bound  in  cloth  and  gold;  price, 
postpaid, $1.50 

Tobacco  Leaf 

By  J.  B.  KILLEBREW  and  HERBERT  MYRICK.  Its  Culture 
and  Cure,  Marketing  and  Manufacture.  A  practical  handbook 
on  the  most  approved  methods  in  growing,  harvesting,  curing, 
packing  and  selling  tobacco,  with  an  account  of  the  opera- 
tions in  every  department  of  tobacco  manufacture.  The 
contents  of  this  book  are  based  on  actual  experiments  in  field, 
curing  barn,  packing  house,  factory  and  laboratory.  It  is  the 
only  work  of  the  kind  in  existence,  and  is  destined  to  be  the 
standard  practical  and  scientific  authority  on  the  whole  sub- 
ject of  tobacco  for  many  years.  506  pages  and  150  original 
engravings.  5  x7  inches.  Cloth.-  .»  .-  .  .  $2.00 


Land  Draining 

A  handbook  for  farmers  on  the  principles  and  practice  of 
draining,  by  MANLY  MILES,  giving  the  results  of  his  extended 
experience  in  laying  tile  drains.  The  directions  for  the  laying 
out  and  the  construction  of  tile  drains  will  enable  the  farmer 
to  avoid  the  errors  of  imperfect  construction,  and  the  disap- 
pointment that  must  necessarily  follow.  This  manual  for 
practical  farmers  will  also  be  found  convenient  for  reference 
in  regard  to  many  questions  that  may  arise  in  crop  growing, 
aside  from  the  special  subjects  of  drainage  of  which  it  treats. 
Illustrated.  200  pages.  5x7  inches.  Cloth.  .  ,  $1.00 

Barn  Plans  and  Outbuildings 

Two  hundred  and  fifty-seven  illustrations.  A  most  valu- 
able work,  full  of  ideas,  hints,  suggestions,  plans,  etc.,  for  the 
construction  of  barns  and  outbuildings,  by  practical  writers. 
Chapters  are  devoted  to  the  economic  erection  and  use  of 
barns,  grain  barns,  horse  barns,  cattle  barns,  sheep  barns,  corn- 
houses,  smokehouses,  icehouses,  pig  pens,  granaries,  etc. 
There  are  likewise  chapters  on  birdhouses,  doghouses,  tool 
sheds,  ventilators,  roofs  and  roofing,  doors  and  fastenings, 
workshops,  poultry  houses,  manure  sheds,  barnyards,  root  pits, 
etc.  235  pages.  5x7  inches.  Cloth.  .  $1.00 

Irrigation  Farming 

By  LUTE  WILCOX.  A  handbook  for  the  practical  applica- 
tion of  water  in  the  production  of  crops.  A  complete  treatise 
on  water  supply,  canal  construction,  reservoirs  and  ponds, 
pipes  for  irrigation  purposes,  flumes  and  their  structure, 
methods  of  applying  water,  irrigation  of  field  crops,  the 
garden,  the  orchard  and  vineyard,  windmills  and  pumps, 
appliances  and  contrivances.  New  edition,  revised,  enlarged 
and  rewritten.  Profusely  illustrated.  Over  500  pages.  5x7 
inches.  Cloth. $2.00 

Forest  Planting 

By  H.  NICHOLAS  JARCHOW,  LL.  D.  A  treatise  on  the  care 
of  woodlands  and  the  restoration  of  the  denuded  timberlands 
on  plains  and  mountains.  The  author  has  fully  described 
those  European  methods  which  have  proved  to  be  most  useful 
in  maintaining  the  superb  forests  of  the  old  world.  This  expe- 
rience has  been  adapted  to  the  different  climates  and  trees  of 
America,  full  instructions  being  given  for  forest  planting  of 
our  various  kinds  of  soil  and  subsoil,  whether  on  mountain 
or  valley.  Illustrated.  250  page s,  5x7  inches.  Cloth.  $1.50 


Animal  Breeding 

By  THOMAS  SHAW.  This  book  is  the  most  complete  and 
comprehensive  work  ever  published  on  the  subject  of  which 
it  treats.  It  is  the  first  book  which  has  systematized  the  subject 
of  animal  breeding.  The  leading  laws  which  govern  this 
most  intricate  question  the  author  has  boldly  defined  and 
authoritatively  arranged.  The  chapters  which  he  has  written 
on  the  more  involved  features  of  the  subject,  as  sex  and  the 
relative  influence  of  parents,  should  go  far  toward  setting  at 
rest  the  wildly  speculative  views  cherished  with  reference  to 
thes.e  questions.  The  striking  originality  in  the  treatment  of 
the  subject  is  no  less  conspicuous  than  the  superb  order  and 
regular  sequence  of  thought  from  the  beginning  to  the  end 
of  the  book.  The  book  is  intended  to  meet  the  needs  of  all 
persons  interested  in  the  breeding  and  rearing  of  live  stock. 
Illustrated.  405  pages.  5x7  inches.  Cloth.  .  .  $1.50 

Forage  Crops  Other  Than  Grasses 

By  THOMAS  SHAW.  How  to  cultivate,  harvest  and  use 
them.  Indian  corn,  sorghum,  clover,  leguminous  plants,  crops 
of  the  brassica  genus,  the  cereals,  millet,  field  roots,  etc. 
Intensely  practical  and  reliable.  Illustrated.  287  pages.  5x7 
inches.  Cloth $1.00 

Soiling  Crops  and  the  Silo 

By  THOMAS  SHAW.  The  growing  and  feeding  of  all  kinds 
of  soiling  crops,  conditions  to  which  they  are  adapted,  their 
plan  in  the  rotation,  etc.  Not  a  line  is  repeated  from  the 
Forage  Crops  book.  Best  methods  of  building  the  silo,  filling 
it  and  feeding  ensilage.  Illustrated.  364  pages.  5x7  inches. 
Cloth. $1.50 

The  Study  of  Breeds 

By  THOMAS  SHAW.  Origin,  history,  distribution,  charac- 
teristics, adaptability,  uses,  and  standards  of  excellence  of  all 
pedigreed  breeds  of  cattle,  sheep  and  swine  in  America.  The 
accepted  text  book  in  colleges,  and  the  authority  for 
farmers  and  breeders.  Illustrated.  371  pages.  5x7  inches. 
Cloth $1-50 

Profits  in  Poultry 

Useful  and  ornamental  breeds  and  their  profitable  man- 
agement. This  excellent  work  contains  the  combined  expe- 
rience of  a  number  of  practical  men  in  all  departments  of 
poultry  raising.  It  forms  a  unique  and  important  addition  to 
our  poultry  literature.  Profusely  illustrated.  352  pages.  5x7 
inches.  Cloth.  . $1.00 


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SEP    10  1832 

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' 


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165149 


